Patent Publication Number: US-2007112250-A1

Title: Insertion support tool for medical instrument and insertion method for medical instrument

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an insertion support tool for a medical instrument and an insertion method for a medical instrument, which support an operation of inserting, e.g., a large-intestine microscope into a body.  
      2. Description of the Related Art  
      At the time of an operation of inserting a large-intestine endoscope into a patient&#39;s body, an operation of inserting an end portion of the endoscope into an anus and further pushing it into a large intestine is carried out. In general, the large intestine has many bent parts in the middle of a long tract and hence has a complicated shape. Therefore, the operation of inserting the endoscope into the large intestine is a relatively difficult operation.  
      As a technology which supports such an operation of inserting the endoscope into the large intestine, International Publication No. 02/19886 discloses an endoscope. In this publication, a bag-shaped exterior sheath is attached in a folded state on an outer side of an elongated inserting portion which is inserted into a body. Further, at the time of an operation of inserting the endoscope, a gas is injected into a bag of the exterior sheath. As a result, the exterior sheath is extended. Furthermore, the endoscope is led into the large intestine by this extending operation of the exterior sheath. Since this exterior sheath is extended by elastically deforming this folded portion, it is desirable for the exterior sheath to have flexibility and to be readily extended.  
      It is normal that the anus of a patient is closed by a sphincter muscle. Therefore, when inserting the endoscope, insertion is carried out while spreading the sphincter muscle of the anus.  
     BRIEF SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide an insertion support tool for a medical instrument and an insertion method for a medical instrument which have been improved in quality.  
      According to a first aspect of the present invention, there is provided an insertion support tool for a medical instrument, comprising: a transforming portion which is expandable and contractible along an inserting direction of an inserting portion of the medical instrument having flexibility into a lumen; and a cylindrical cover member which is held to cover the transforming portion when the transforming portion is contracted.  
      The cover member may be formed of a material which can prevent an external force applied to a surface of this cover member from acting on the transforming portion.  
      The transforming portion may have a bag-shaped sheath which is arranged to cover at least a part of a side surface of the inserting portion in the inserting direction and which is extendable in the inserting direction of the inserting portion by supply of a fluid.  
      The insertion support tool may further have a holding member which maintains a state where the cover member covers the transforming portion when the transforming portion is contracted.  
      The holding member may have a packing material which is used to pack the insertion support tool.  
      The insertion support tool may further comprise a protection member including a fixing portion at which at least a part of the insertion support tool is fixed, and the protection member may be inserted into and fixed in the lumen prior to insertion of the medical instrument into the lumen.  
      According to a second aspect of the present invention, there is provided an insertion support tool for a medical instrument, which is detachably attached to the medical instrument including a shaft-shaped inserting portion having flexibility which is inserted into a lumen, comprising: a bag-shaped transforming portion which is arranged outside the insertion portion and which is extendable in an inserting direction of the inserting portion by supply of a fluid; a base unit having a first transforming portion fixing portion at which a base end portion of the transforming portion is fixed; an end unit having a second transforming portion fixing portion at which an end portion of the transforming portion is fixed; and a cylindrical cover member which is arranged outside the transforming portion, whose base end portion is fixed to the based unit, and which is held to cover the transforming portion when the transforming portion is contracted.  
      The transforming portion may have an outer sheath having a folded first bellows portion and an inner sheath which is arranged in the outer sheath and has a folded second bellows portion, and the base unit may have a fluid path through which a working fluid is supplied between the outer sheath and the inner sheath.  
      The end unit may have an engagement member which is releasably engaged with an end portion of the cover member and maintains the state where the cover member covers the transforming portion when the transforming portion is contracted.  
      The engagement member may have a tape which locks a part between the end unit and the cover member.  
      The engagement member may have a fixed thread having one end fixed to the end unit and the other end fixed to the base unit.  
      The engagement member may have a concavoconvex fitting portion which is formed at a joint portion of the end unit and the cover member.  
      According to a third aspect of the present invention, there is provided an insertion method for a medical instrument, comprising: a step of attaching an insertion support tool to the medical instrument including a shaft-shaped inserting portion which is inserted into a lumen; a first insertion step of inserting the insertion support tool together with the medical instrument into the lumen while maintaining a state where a cylindrical cover member covers a transforming portion which is extendable and contractible in an inserting direction of the insertion portion after attaching the insertion support tool; and a second insertion step of fixing a base end portion of the insertion support tool in an anus part, then extending the transforming portion in the inserting direction of the insertion portion to protrude the medical instrument from the cover member so that the medical instrument is moved forward in the inserting direction of the inserting portion.  
      According to a fourth aspect of the present invention, there is provided an insertion support tool for a medical instrument, having: a first extension unit which is extendable and contractible in an inserting direction of an inserting portion of the medical instrument having flexibility into a lumen; a second extension unit which is extendable and contractible in the inserting direction separately from the first extension unit; and a coupling member which couples the first extension unit with the second extension unit.  
      The second extension unit may be arranged at an end portion of the first extension unit.  
      The first extension unit may comprise: a bag-shaped first transforming portion which is arranged to cover at least a part of a side surface of the inserting portion in the inserting direction and which is extendable in the inserting direction by supply of a fluid; a base unit having a first transforming portion fixing portion to which a base end portion of the first transforming portion is fixed; an end unit having a second transforming portion fixing portion to which an end portion of the first transforming portion is fixed; and a cylindrical cover member whose end portion is fixed to the end unit and which is maintained to cover the first transforming portion when the first transforming portion is contracted, the second extension unit may have: a bag-shaped second transforming portion which is arranged to cover at least a part of the side surface of the inserting portion in the inserting direction and which is extendable in the inserting direction by supply of a fluid; a cylindrical rear side frame member coupled with a base end portion of this second transforming portion; and an end side frame member coupled with an end portion of the second transforming portion, and the coupling member may have a coupling tube whose end is fixed to the rear side frame member and whose base end is fixed to the end unit.  
      The first transforming portion may have a first outer sheath having a folded first bellows portion and a first inner sheath which is arranged on the inner side of the first outer sheath and has a folded second bellows portion, the base unit may have a first fluid path through which a working fluid is supplied between the first outer sheath and the first inner sheath, the second transforming portion may have a second outer sheath having a folded third bellows sheath portion and a second inner sheath which is arranged on the inner side of this second outer sheath and has a folded fourth bellows portion, and the rear side frame member may have a second fluid path through which a working fluid is supplied between the second outer sheath and the second inner sheath.  
      The insertion support tool may have an indicating portion which indicates identification data of the medical instrument to be combined.  
      According to a fifth aspect of the present invention, there is provided an insertion method for a medical instrument, comprising: a step of attaching an insertion support tool to the medical instrument including a shaft-shaped inserting portion having flexibility which is inserted into a lumen; a first insertion step of inserting the insertion support tool together with the medical instrument into the lumen after attaching the insertion support tool; a second insertion step of fixing a base end portion of the insertion support tool in an anus part, and then extending the first transforming portion in an inserting direction of the inserting portion to move forward the medical instrument in the inserting direction of the inserting portion; and a third insertion step of extending the second transforming portion in the inserting direction of the inserting portion to move forward the medical instrument in the inserting direction of the inserting portion independently of the forward movement operation of the medical instrument by the first transforming portion.  
      Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a vertical cross-sectional view showing an outline configuration of an insertion support tool for a large-intestine endoscope according to a first embodiment of the present invention;  
       FIG. 2  is a vertical cross-sectional view showing a state in which the endoscope is assembled with respect to the insertion support tool according to the first embodiment;  
       FIG. 3A  is a schematic block diagram showing a state before an assembled unit in which the endoscope is assembled with respect to the insertion support tool according to the first embodiment is inserted into an anus;  
       FIG. 3B  is a schematic block diagram showing a state in which the assembled unit is inserted into the anus;  
       FIG. 4  is a vertical cross-sectional view showing a state in which the assembled unit including the insertion support tool according to the first embodiment and the endoscope is extended in a large intestine;  
       FIG. 5  is an explanatory view illustrating a state of coupling an air supply tube with an air supply mouthpiece of a base unit of the insertion support tool according to the first embodiment;  
       FIG. 6  is a schematic block diagram showing a use state of a support member of the endoscope assembled with respect to the insertion support tool according to the first embodiment;  
       FIG. 7A  is a perspective view of a primary part showing an example of the support member of the endoscope;  
       FIG. 7B  is a perspective view of a primary part showing a modification of the support member of the endoscope;  
       FIG. 8  is a vertical cross-sectional view showing an outline configuration of an insertion support tool for a large-intestine endoscope according to a second embodiment of the present invention;  
       FIG. 9  is a schematic block diagram showing a state where an assembled unit in which the endoscope is assembled with respect to the insertion support tool according to the second embodiment is inserted into an anus;  
       FIG. 10  is a vertical cross-sectional view showing a primary part configuration of an insertion support tool according to a third embodiment of the present invention;  
       FIG. 11  is an explanatory view illustrating a primary part configuration of an insertion support tool according to a fourth embodiment of the present invention;  
       FIG. 12  is a vertical cross-sectional view showing a primary part configuration of an endoscope insertion apparatus according to a fifth embodiment of the present invention;  
       FIG. 13  is a side view showing a primary part configuration of an insertion support tool according to the fifth embodiment;  
       FIG. 14  is an explanatory view illustrating a primary part configuration of an insertion support tool according to a sixth embodiment of the present invention;  
       FIG. 15  is a side view showing an unsealing portion of a packing bag of the insertion support tool according to the sixth embodiment;  
       FIG. 16  is an explanatory view illustrating an assembling operation of assembling an endoscope with respect to the insertion support tool from the unsealing portion of the packing bag of the insertion support tool according to the sixth embodiment;  
       FIG. 17  is an explanatory view illustrating a first modification of the packing bag of the insertion support tool according to the sixth embodiment;  
       FIG. 18  is a plan view showing a second modification of the packing bag of the insertion support tool according to the sixth embodiment;  
       FIG. 19  is a plan view showing a third modification of the packing bag of the insertion support tool according to the sixth embodiment;  
       FIG. 20A  is a perspective view showing a fourth modification of the packing bag of the insertion support tool according to the sixth embodiment in a state where the insertion support tool is enclosed in the packing bag;  
       FIG. 20B  is an explanatory view illustrating an operation of taking out the insertion support tool from the packing bag of the fourth modification;  
       FIG. 21A  is a perspective view showing a fifth modification of the packing bag of the insertion support tool according to the sixth embodiment in a state where the insertion support tool is enclosed in the packing bag;  
       FIG. 21B  is an explanatory view illustrating an operation of taking out the insertion support tool from the packing bag of the fifth modification;  
       FIG. 22  is a vertical cross-sectional view of a primary part showing an insertion support tool according to a seventh embodiment of the present invention;  
       FIG. 23  is a front view showing an endoscope fixing portion of the insertion support tool according to the seventh embodiment;  
       FIG. 24  is a perspective view showing the endoscope fixing portion of the insertion support tool according to the seventh embodiment;  
       FIG. 25  is a perspective view showing an end portion of an inserting portion of an endoscope which is assembled with respect to the insertion support tool according to the seventh embodiment;  
       FIG. 26  is a perspective view showing a base unit of the insertion support tool according to the seventh embodiment;  
       FIG. 27A  is a front view showing a pressed state of an operation button of an endoscope pressing portion in the base unit of the insertion support tool according to the seventh embodiment;  
       FIG. 27B  is a vertical cross-sectional view of a primary part showing the pressed state of the operation button according to the seventh embodiment;  
       FIG. 28  is a vertical cross-sectional view of a primary part showing a first modification of the endoscope pressing portion of the insertion support tool according to the seventh embodiment;  
       FIG. 29  is a vertical cross-sectional view of a primary part showing a pressing released state of the operation button in the first modification of the insertion support tool according to the seventh embodiment;  
       FIG. 30A  is a lateral cross-sectional view of a primary part of a second modification of the endoscope pressing portion of the insertion support tool according to the seventh embodiment;  
       FIG. 30B  is a lateral cross-sectional view of a primary part showing a third modification of the endoscope pressing portion;  
       FIG. 31A  is a vertical cross-sectional view of a primary part showing a fixing released state of an endoscope pressing portion according to an eighth embodiment of the present invention;  
       FIG. 31B  is a vertical cross-sectional view of a primary part showing a fixing state of an endoscope by the endoscope pressing portion according to the eighth embodiment;  
       FIG. 32  is a vertical cross-sectional view of a primary part showing an endoscope pressing portion of an insertion support tool according to a ninth embodiment of the present invention;  
       FIG. 33  is a vertical cross-sectional view of a primary part showing an endoscope pressing portion of an insertion support tool according to a 10th embodiment of the present invention;  
       FIG. 34  is a lateral cross-sectional view of a primary part showing an endoscope pressing portion of an insertion support tool according to an 11th embodiment of the present invention;  
       FIG. 35A  is a perspective view of a primary part showing a state where an adhesive tape is attached on a flange portion of an insertion support tool according to a 12th embodiment of the present invention;  
       FIG. 35B  is a vertical cross-sectional view of a primary part showing the flange portion of the insertion support tool according to the 12th embodiment;  
       FIG. 35C  is a schematic block diagram of a primary part showing a state where the flange portion of the insertion support tool according to the 12th embodiment is fixed to a patient;  
       FIG. 35D  is an explanatory view illustrating an operation of inserting the insertion support tool according to the 12th embodiment into the patient;  
       FIG. 35E  is an explanatory view illustrating a curved state of the insertion support tool inserted into the patient according to the 12th embodiment;  
       FIG. 36A  is a vertical cross-sectional view of a peripheral part of the flange portion, showing a modification of the flange portion of the insertion support tool according to the 12th embodiment;  
       FIG. 36B  is a perspective view showing the flange portion of the insertion support tool according to the same modification;  
       FIG. 37  is a vertical cross-sectional view of a primary part showing an insertion support tool according to a 13th embodiment of the present invention;  
       FIG. 38A  is a schematic block diagram of a primary part showing a state where an insertion support tool according to a 14th embodiment of the present invention is fixed to a patient;  
       FIG. 38B  is a schematic block diagram of a primary part showing a state where a fixing belt is disposed to an attachment groove of the insertion support tool according to the 14th embodiment;  
       FIG. 39  is a vertical cross-sectional view of a primary part showing an insertion support tool according to a 15th embodiment of the present invention;  
       FIG. 40  is a side view showing the insertion support tool according to the 15th embodiment;  
       FIG. 41A  is a view showing a state where a treatment instrument in an observation image of an endoscope inserted into a body by the insertion support tool according to the 15th embodiment appears from a lower side of a screen;  
       FIG. 41B  is a view showing a state where the treatment instrument appears from an upper side of the screen;  
       FIG. 41C  is a view showing a state where the treatment instrument appears from a left side of the screen;  
       FIG. 42  is a plan view of a primary part showing an insertion support tool according to a 16th embodiment of the present invention;  
       FIG. 43  is a plan view of a primary part showing an insertion support tool according to a 17th embodiment of the present invention;  
       FIG. 44  is a plan view of a primary part showing an insertion support tool according to an 18th embodiment of the present invention;  
       FIG. 45  is a plan view of a primary part showing an insertion support tool according to a 19th embodiment of the present invention;  
       FIG. 46A  is a side view showing a state where the insertion support tool is twisted at the time of an operation of the insertion support tool according to the 19th embodiment;  
       FIG. 46B  is a vertical cross-sectional view of  FIG. 46A ;  
       FIG. 47  is a plan view of a primary part showing an insertion support tool according to a 20th embodiment of the present invention;  
       FIG. 48  is a plan view of a primary part showing an insertion support tool according to a 21st embodiment of the present invention;  
       FIG. 49  is a schematic block diagram of an insertion support tool of a large-intestine endoscope according to a 22nd embodiment of the present invention;  
       FIG. 50  is a vertical cross-sectional view showing an end side extension unit of the insertion support tool according to the 22nd embodiment;  
       FIG. 51A  is an explanatory view illustrating a state where an end portion of the large-intestine endoscope has reached a position of a sharp intestinal canal bent part at the time of an operation of inserting the large-intestine endoscope into the large intestine by the insertion support tool according to the 22nd embodiment;  
       FIG. 51B  is an explanatory view illustrating a state where a curving portion of the large-intestine endoscope lodges in the sharp intestinal canal bent part and cannot advance even though a main extension unit is extended;  
       FIG. 51C  is an explanatory view illustrating a state of extending a second transforming portion in an inserting direction of an inserting portion by an operation of pushing out an elongated inserting portion of a medical instrument in the inserting direction of the inserting portion;  
       FIG. 52  is an explanatory view illustrating a primary part configuration of an insertion support tool according to a 23rd embodiment of the present invention;  
       FIG. 53A  is a side view of a primary part showing a state where a roller fixing lever is engaged with a wire fixing portion of the insertion support tool according to the 23rd embodiment;  
       FIG. 53B  is a plan view of  FIG. 53A ;  
       FIG. 53C  is a side view of a primary part showing a state where the roller fixing lever has released engagement with the wire fixing portion;  
       FIG. 54A  is a vertical cross-sectional view of a primary part showing a wire fixing state of a first modification of the wire fixing portion assembled in the insertion support tool according to the 23rd embodiment;  
       FIG. 54B  is a cross-sectional view taken along a line  54 B- 54 B in  FIG. 54A ;  
       FIG. 55A  is a vertical cross-sectional view of a primary part showing a wire fixing released state where a wire fixing claw in the first modification of the wire fixing portion is broken off;  
       FIG. 55B  is a front view of  FIG. 55A ;  
       FIG. 56A  is a vertical cross-sectional view of a primary part showing a wire fixing state in a second embodiment of the wire fixing portion according to the 23rd embodiment;  
       FIG. 56B  is a vertical cross-sectional view of a primary part showing a wire fixing released state;  
       FIG. 57  is a vertical cross-sectional view of a primary art showing a state where an end side extension unit of an insertion support tool according to a 24th embodiment of the present invention is not used;  
       FIG. 58  is a vertical cross-sectional view of a primary part showing a state where the end side extension unit of the insertion support tool according to the 24th embodiment is used;  
       FIG. 59  is an explanatory view illustrating a primary part configuration of an insertion support tool according to a 25th embodiment of the present invention;  
       FIG. 60  is a vertical cross-sectional view showing a primary part configuration of a driving device for the end side extension unit of the insertion support tool according to the 25th embodiment;  
       FIG. 61  is a side view showing a state where the end side extension unit of the insertion support tool according to the 25th embodiment is extended;  
       FIG. 62A  is a schematic block diagram showing a state where the end side extension unit is extended at the time of an operation of the insertion support tool according to the 25th embodiment;  
       FIG. 62B  is a schematic block diagram showing a state where the end side extension unit is contracted;  
       FIG. 63  is a vertical cross-sectional view showing a modification of a driving device of the end side extension unit of the insertion support tool according to the 25th embodiment;  
       FIG. 64  is vertical cross-sectional view of a primary part showing a state where an endoscope is assembled with respect to an insertion support tool according to a 26th embodiment of the present invention;  
       FIG. 65  is an explanatory view illustrating an operation of the insertion support tool according to the 26th embodiment;  
       FIG. 66  is a vertical cross-sectional view of a primary part showing a state where an endoscope is assembled with respect to an insertion support tool according to a 27th embodiment of the present invention;  
       FIG. 67  is an explanatory view illustrating an operation of the insertion support tool according to the 27th embodiment;  
       FIG. 68A  is a vertical cross-sectional view of a primary part of an insertion support tool according to a 28th embodiment of the present invention;  
       FIG. 68B  is an explanatory view illustrating an operation of a driving device for an end side extension unit according to the 28th embodiment;  
       FIG. 69  is a vertical cross-sectional view of a primary part showing an insertion support tool according to a 29th embodiment of the present invention; and  
       FIG. 70  is a side view showing the insertion support tool according to the 29th embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A first embodiment according to the present invention will now be described hereinafter with reference to FIGS.  1  to  7 A.  FIG. 1  shows an endoscope insertion apparatus  1  as an insertion apparatus for a medical instrument according to this embodiment. The endoscope insertion apparatus  1  has an insertion support tool  4  which is detachably attached at an end portion of an inserting portion  3  of a large-intestine endoscope  2 .  
      As shown in  FIG. 5 , the large-intestine endoscope  2  has the elongated shaft-shaped inserting portion  3  which is inserted into a body and an operating portion with a large diameter which is arranged at a base end portion of the inserting portion  3 . As shown in  FIG. 2 , the inserting portion  3  has an elongated flexible tube portion  6 , a curving portion  7  which can curve in, e.g., four directions, i.e., up, down, right and left directions, and an end hard portion  8 . Further, the base end portion of the flexible tube portion  6  is coupled with the operating portion  5 . An end portion of a non-illustrated curving operation wire is coupled with the curving portion  7 .  
      As shown in  FIG. 25 , an end surface of the end hard portion  8  has at least one observation window  9  and two illumination windows  10  and  11 . An objective lens is arranged behind a cover glass of the observation window  9 . An imaging element such as a CCD is arranged at an image forming position of this objective lens. One end portion of a signal cable is connected with this imaging element. An end portion of a light guide fiber bundle is arranged behind cover glasses of the illumination windows  10  and  11 .  
      Furthermore, the signal cable of the imaging element, the light guide fiber bundle, the curving operation wire and others are extended to the operating portion  5  side through the inserting portion  3 . Moreover, the signal cable of the imaging element, the light guide fiber bundle, the curving operation wire and others are packaged as built-in members in the inserting portion  3 .  
      A curving operation knob  12  which operates the curving portion  7  is arranged on the operating portion  5 . A central shaft of the curving operation knob  12  is coupled with a curving operation mechanism included in the operating portion  5 . A base end portion of the curving operation wire is coupled with this curving operation mechanism. Additionally, the curving operation wire is towed by a rotating operation of the curving operation knob  12  via the curving operation mechanism, and the curving portion  7  is remotely operated in an operating direction of the curving operation knob  12 .  
      Further, one end portion of a universal cord  13  is coupled with the operating portion  5 . A light connector and an electric signal connector are provided at the other end portion of this universal cord  13 . The light connector is connected with a light source device and the electric signal connector is connected with a video processor, respectively. Here, the signal cable or the light guide fiber bundle is inserted into the universal cord  13  from the operating portion  5 . Furthermore, the signal cable is connected with the electric signal connector.  
      Moreover, the other end portion of the light guide fiber bundle is connected with the light connector. Illumination light emitted from a light source lamp of the light source device is led to the end hard portion  8  side of the inserting portion  3  through the light guide fiber bundle, and then emitted toward the outside from the illumination windows  10  and  11 . Additionally, an observation image which has entered from the observation window  9  is converted into an electric signal by the imaging element at the image forming position of the objective lens. This electric signal is input to the video processor through the signal cable and signal-processed by the video processor, and a video signal is supplied to a non-illustrated monitor so that an image is displayed in a screen of the monitor.  
      Further, the insertion support tool  4  has a soft bag-shaped external sheath (a transforming portion)  14  which can be extended along an inserting direction of the inserting portion  3  of the large-intestine endoscope  2 , a base unit  15  coupled with a base end portion of this external sheath  14 , and an end unit  16  coupled with an end portion of the external sheath  14 .  
      The base unit  15  has a substantially cylindrical mouthpiece member  17 . The inserting portion  3  of the large-intestine endoscope  2  can be inserted into a cylinder of this mouthpiece member  17 . A large-diameter portion  17   a  having the largest diameter is provided on an outer peripheral surface of the mouthpiece member  17  on the base end portion side thereof. An end cylindrical portion  17   b  having a diameter smaller than that of any other part is provided on an end portion side of the mouthpiece member  17 . A diameter of a cylinder of this end cylindrical portion  17   b  is set to a dimension which allows insertion of the inserting portion  3  of the large-intestine endoscope  2 .  
      Two step portions  17   c  and  17   d  having different outer diameters are formed between the large-diameter portion  17   a  and the end cylindrical portion  17   b  of the mouthpiece member  17 . The large-diameter step portion  17   c  having a large diameter is arranged on the base end portion side of the mouthpiece member  17 , and the small-diameter step portion  17   d  having a diameter smaller than that of the large-diameter step portion  17   c  is arranged on the end portion side apart from this large-diameter step portion  17   c.    
      Furthermore, the external sheath  14  has an outer sheath  18  and an inner sheath  19 . A rear side fixing ring  18   a  is formed at a base end portion of the outer sheath  18 . The rear side fixing ring  18   a  is fixed at the small-diameter step portion  17   d  of the mouthpiece member  17 . Moreover, an end side of the outer sheath  18  is extended toward the end unit  16  side. Additionally, a folded first bellows portion  18   b  is formed on this extended portion side.  
      A folded second bellows portion  19   a  is formed in the inner sheath  19 . This second bellows portion  19   a  is arranged on the end cylindrical portion  17   b  of the mouthpiece member  17 . Further, a rear side fixing ring  19   b  which is fixed at a base end portion of the end cylindrical portion  17   b  is formed at a base end portion of this second bellows portion  19   a.    
      The end unit  16  has an external sheath fixing member  20 , a hard end member  21  and a soft coupling tube  22 . The external sheath fixing member  20  has an inner cylindrical portion  20   a  whose diameter is substantially the same as that of the end cylindrical portion  17   b  of the mouthpiece member  17 , and an outer cylindrical portion  20   b  whose diameter is larger than that of this inner cylindrical portion  20   a . An outer diameter of the outer cylindrical portion  20   b  is set to be substantially equal to that of the large-diameter step portion  17   c  of the mouthpiece member  17 .  
      A bent portion  20   c  which is inwardly bent is formed at an end portion of the outer cylindrical portion  20   b . An inner end portion of this bent portion  20   c  is fixed on an outer peripheral surface of the inner cylindrical portion  20   a . Furthermore, an annular first flange portion  23  having a large diameter is formed to protrude on an outer peripheral surface of the outer cylindrical portion  20   b  on a base end portion side thereof.  
      An annular second flange portion  24  having a large diameter is formed to protrude on an outer peripheral surface of the inner cylindrical portion  20   a  on a base end portion side thereof. Moreover, an outer sheath accommodation space  25  is formed in front of the second flange portion  24  between the inner cylindrical portion  20   a  and the outer cylindrical portion  20   b . The first bellows portion  18   b  of the outer sheath  18  is accommodated in this outer sheath accommodation space  25 . A front side fixing ring  18   c  which is fixed at the end portion of the inner cylindrical portion  20   a  is formed at an end portion of this first bellows portion  18   b . A front side fixing ring  19   c  which is fixed on the outer peripheral surface of the inner cylindrical portion  20   a  is formed at the end portion of the second bellows portion  19   a  in the inner sheath  19 . This front side fixing ring  19   c  is arranged on a rear side apart from the second flange portion  24  of the inner cylindrical portion  20   a.    
      Additionally, a fluid path  26  through which a working fluid such as pressurized air is supplied is formed in the mouthpiece member  17  between the outer sheath  18  and the inner sheath  19  of the external sheath  14 . An inner end portion of this fluid path  26  communicates with a part between the outer sheath  18  and the inner sheath  19  of the mouthpiece member  17 . Further, an outer end portion of the fluid path  26  is coupled with an air supply mouthpiece  27  arranged on the outer peripheral surface of the mouthpiece member  17  as shown in  FIG. 5 . One end portion of an air supply tube  28  is coupled with this air supply mouthpiece  27 . The other end portion of this air supply tube  28  is coupled with a non-illustrated air supply pump. Furthermore, a working fluid such as pressurized air is supplied to a part between the outer sheath  18  and the inner sheath  19  from this air supply tube  28  through the air supply mouthpiece  27  and the fluid path  26  when the external sheath  14  of the insertion support tool  4  is extended. At this time, the external sheath  14  is extended in the inserting direction of the inserting portion  3  by a supply pressure of the working fluid (see  FIG. 4 ).  
      Moreover, a cylindrical hard cover member  29  is arranged around the external sheath  14 . This cover member  29  is formed of a hard material such as a hard rubber material, a plastic material, a composite material in which a soft rubber material covers a surface of a cored bar, or the like. A base end portion of the cover member  29  is fixed at the large-diameter step portion  17   c  of the mouthpiece member  17 . An end portion of this cover member  29  is extended toward the end unit  16  side. Additionally, as shown in  FIG. 1 , when the external sheath  14  is contracted, the end portion of the cover member  29  is maintained in a state where it is in contact with the first flange portion  23  of the end unit  16 . In this state, the cover member  29  keeps covering the external sheath  14 . A length of the cover member  29  is set to a length which allows the end portion of the cover member  29  to enter a large intestine (a rectum) H 2  beyond an anus H 1 , e.g., 3 cm or below when the insertion support tool  4  is inserted into the large-intestine (the rectum) H 2  from the anus H 1  of a patient H.  
      Further, to the insertion support tool  4  is provided an adhesive tape (engagement means)  30  as a holding member which holds the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 . An end portion side of this adhesive tape  30  is attached and fixed at the end unit  16 , and a base end portion side of the same is attached and fixed at the cover member  29 . As a result, when the external sheath  14  is contracted, this adhesive tape  30  maintains an engaged state where the end portion of the cover member  29  is releasably engaged with the end unit  16 .  
      Furthermore, the end member  21  has an endoscope attachment hole  31  at a substantial shaft center portion thereof. A front side of this endoscope attachment hole  31  is sealed by a transparent cover glass  32 . Moreover, the end hard portion  8  of the inserting portion  3  of the large-intestine endoscope  2  can be coupled with the endoscope attachment hole  31  of the end member  21  in a fitting state.  
      The soft coupling tube  22  is stretched between the end member  21  and the outer cylindrical portion  20   b  of the external sheath fixing member  20 . This coupling tube  22  is arranged at a position corresponding to the curving portion  7  of the large-intestine endoscope  2  in a state where the insertion support tool  4  is assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2 . Therefore, the coupling tube  22  can freely transform in accordance with a curving operation of the curving portion  7  of the large-intestine endoscope  2 .  
      A function of the above-mentioned structure will now be described. The endoscope insertion apparatus  1  according to this embodiment is used in a state where the insertion support tool  4  is attached to the inserting portion  3  of the large-intestine endoscope  2  when utilizing the large-intestine endoscope  2 .  
       FIG. 1  shows a state before the insertion support tool  4  is assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2 . At this time, the insertion support tool  4  is maintained in a state where the external sheath  14  is previously contracted and the hard cover member  29  is arranged on the outer side of the external sheath  14  to cover the external sheath  14 . Here, the external sheath  14  is maintained in a state where the second bellows portion  19   a  of the inner sheath  19  is folded and arranged on the end cylindrical portion  17   b  of the mouthpiece member  17  in the folded manner and the first bellows portion  18   b  of the outer sheath  18  is folded and accommodated in the outer sheath accommodation space  25  between the inner cylindrical portion  20   a  and the outer cylindrical portion  20   b  of the external sheath fixing member  20  in the folded manner. Additionally, the adhesive tape  30  maintains an engaged state where the end portion of the cover member  29  is releasably engaged with the end unit  16 . In this state, there is carried out an operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  (an insertion support tool attachment step).  
      In this insertion support tool attachment operation, the inserting portion  3  of the large-intestine endoscope  2  is inserted from the end side thereof into the cylinder of the mouthpiece member  17  from an opening portion  17   e  on a base end surface of the mouthpiece member  17  of the insertion support tool  4 . Further, the end hard portion  8  of the inserting portion  3  is coupled with the endoscope attachment hole  31  of the end member  21  in a fitting state as shown in  FIG. 2 , and an assembled unit  33  having the insertion support tool  4  assembled at the end part of the inserting portion  3  of the large-intestine endoscope  2  is set as shown in  FIG. 3A .  
      After attachment of this insertion support tool  4 , the assembled unit  33  is inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H (a first insertion step). In this inserting operation, the insertion support tool  4  is inserted into the anus H 1  of the patient H from the end member  21  side of the insertion support tool  4 . At this time, since the anus H 1  of the patient H is usually closed by a sphincter muscle, the assembled unit  33  is pushed into the anus H 1  of the patient H while spreading this sphincter muscle of the anus H 1 .  
      Furthermore, during the operation of inserting the assembled unit  33 , the adhesive tape  30  is unstuck from the insertion support tool  4  when the end portion of the adhesive tape  30  has come close to the anus H 1 . As a result, engagement between the end portion of the cover member  29  and the end unit  16  is released.  
      Thereafter, the operation of pushing the assembled unit  33  into the anus H 1  of the patient H is continued. At this time, since the end portion of the cover member  29  is in contact with the first flange portion  23  of the end unit  16 , a pushing force from the cover member  29  side is transmitted to the end unit  16  through the first flange portion  23 . Therefore, the operation of inserting the assembled unit  33  in which the insertion support tool  4  is assembled together with the inserting portion  3  of the large-intestine endoscope  2  is continued like before the adhesive tape  30  is unstuck.  
      Moreover, as shown in  FIG. 3B , the assembled unit  33  is inserted to a position at which the end portion of the cover member  29  of the insertion support tool  4  passes the anus H 1 . In this state, the cover member  29  of the insertion support tool  4  is fixed in the anus H 1  by a fastening force of the sphincter muscle of the anus H 1 .  
      Additionally, after the cover member  29  of the insertion support tool  4  is fixed in the anus H 1 , a working fluid such as pressurized air is supplied from the air supply tube  28  to a part between the outer sheath  18  and the inner sheath  19  through the air supply mouthpiece  27  and the fluid path  26 . At this time, a space between the outer sheath  18  and the inner sheath  19  of the external sheath  14  is inflated by supply of the working fluid. Therefore, as shown in  FIG. 4 , the entire external sheath  14  is extended in the inserting direction of the inserting portion  3  of the large-intestine endoscope  2 . As a result, the insertion support tool  4  moves forward in a state where the end unit  16  is pushed frontward with respect to the base unit  15 . At this time, the inserting portion  3  of the large-intestine endoscope  2  advances together with the end unit  16  in the inserting direction of the inserting portion  3  (a second insertion step).  
      Further,  FIG. 6  shows a state in which the assembled unit  33  having the insertion support tool  4  assembled with respect to the inserting portion  3  of the large-intestine endoscope  4  is inserted into the patient H lying down on a bed  34 . Here, a stand  35  for supporting a medical instrument is provided on the bed  34 . A substantially U-shaped support frame  36  is provided at an upper end portion of this stand  35  as shown in  FIG. 7A . Furthermore, the mouthpiece member  17  of the insertion support tool  4  is supported in a state where it is releasably engaged with the support frame  36  of the stand  35 . It is to be noted that, like a modification shown in  FIG. 7B , a folded portion  36   a  for retention having elasticity may be provided to the support frame  36  of the stand  35  on an opening end portion side.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope insertion apparatus  1  according to this embodiment, attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  can extend the soft external sheath  14  of the insertion support tool  4  in the inserting direction of the inserting portion  3  when inserting the inserting portion  3  of the large-intestine endoscope  2 , thus supporting the inserting operation of the inserting portion  3  of the large-intestine endoscope  2 . Therefore, the operation of inserting the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (the rectum) H 2  of the patient H can be facilitated.  
      Moreover, when the external sheath  14  of the insertion support tool  4  is contracted, the hard cover member  29  on the outer side of the external sheath  14  can be maintained to cover the external sheath  14 . Therefore, at the time of the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2 , this operation can be performed in a state where the hard cover member  29  is grasped. As a result, since a force of an operator who holds the insertion support tool  4  by hand does not directly act on the external sheath  4  during the operation of attaching the insertion support tool  4 , the external sheath  14  is not unnecessarily extended. As a result, the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  can be facilitated.  
      Additionally, at the time of the operation of inserting the assembled unit  33  in which the insertion support tool  4  is assembled with respect to the end part of the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H, the fastening force of the sphincter muscle of the anus H 1  can be received by the cover member  29  of the insertion support tool  4 . Therefore, during the operation of inserting the assembled unit  33  into the anus H 1  of the patient H, the soft external sheath  14  is not crushed or bent by the fastening force of the sphincter muscle of the anus H 1 . As a result, the operation of inserting the assembled unit  33  into the anus H 1  of the patient H can be smoothly and assuredly performed. Further, since the external sheath  14  is not exposed in a state where the external sheath  14  of the insertion support tool  4  is contracted, the external sheath  14  is not damaged before use.  
      Furthermore, in this embodiment, to the insertion support tool  4  is provided the adhesive tape  30  which holds the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 . Therefore, since the external sheath  14  is not unnecessarily extended during the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2 , the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  can be further readily carried out.  
       FIGS. 8 and 9  show a second embodiment according to the present invention. In this embodiment, the configuration of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the first embodiment (see FIGS.  1  to  7 A) is changed as follows.  
      That is, the first embodiment shows a configuration using the adhesive tape  30  as engagement means which holds the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 . On the contrary, an insertion support tool  4  according to this embodiment has a configuration in which a fixed thread  41  is used in place of this adhesive tape  30 . An end portion of this fixed thread  41  is fixed at an outer cylindrical portion  20   b  of an external sheath fixing member  20  of an end unit  16 . A base end portion of this fixed thread  41  is fixed at a mouthpiece member  17  or a rear end portion of a cover member  29 . When attaching this fixed thread  41 , the fixed thread  41  is pulled and fixed in a state where an end portion of the cover member  29  is in contact with a first flange portion  23  of the end unit  16 . As a result, even in a state where the fixed thread  41  is fully stretched, the cover member  29  and the end unit  16  are not separated from each other.  
      A function of this embodiment having the above-mentioned configuration will now be described. In this embodiment, in the insertion support tool  4 , an external sheath  14  is previously contracted before use. Additionally, the hard cover member  29  is maintained arranged on the outer side of the external sheath  14  in a state where the external sheath  14  is covered. At this time, the fixed thread  41  maintains an engagement state in which the end portion of the cover member  29  is releasably engaged with the end unit  16 . In this state, there are carried out the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  (an insertion support tool attachment step) and the operation of inserting the assembled unit  33  in which the insertion support tool  4  is assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H (a first insertion step).  
      Further, during the operation of inserting the assembled unit  33 , as shown in  FIG. 9 , the end portion of the cover member  29  is inserted into the anus H 1 , and then the fixed thread  41  is cut when the base end portion of the fixed thread  41  has come close to the anus H 1 . As a result, engagement between the end portion of the cover member  29  and the end unit  16  is released.  
      Thereafter, supply of a working fluid such as pressurized air to a part between the outer sheath  18  and the inner sheath  19  of the external sheath  14  can extend the entire external sheath  14  in the inserting direction of the inserting portion  3  of the large-intestine endoscope  2 . As a result, the insertion support tool  4  moves forward in a state where the end unit  16  is pushed forward with respect to the base unit  15 . At this time, the inserting portion  3  of the large-intestine endoscope  2  is moved forward together with the end unit  16  in the inserting direction of the inserting portion  3  (a second insertion step).  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope insertion apparatus  1  according to this embodiment, the fixed thread  41  is used as engagement means for holding the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 . Therefore, during the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2 , the external sheath  14  is not unnecessarily extended, and hence it is possible to readily perform the operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  and the operation of inserting the assembled unit  33  having the insertion support tool  4  assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H (the first insertion step) like the first embodiment.  
      Furthermore, in a state where the external sheath  14  of the insertion support tool  4  is contracted, the soft external sheath  14  is covered with the cover member  29 . Therefore, since the soft external sheath  14  is not exposed to the outside, the external sheath  14  is not damaged before use.  
      Moreover,  FIG. 10  shows a third embodiment according to the present invention. In this embodiment, the configuration of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the first embodiment (see FIGS.  1  to  7 A) is changed as follows.  
      That is, in this embodiment, an annular engagement protrusion  51  which protrudes in an inner direction is provided on an end portion inner peripheral surface of a cover member  29  of an insertion support tool  4 . Additionally, an annular locking concave portion  52  is formed on a base end portion outer peripheral surface of an outer cylindrical portion  20   b  of an end unit  16  behind a first flange portion  23 . Further, a rear end flange portion  53  having a diameter larger than that of the locking concave portion  52  is protrudingly provided behind this locking concave portion  52 .  
      Furthermore, the engagement protrusion  51  of the cover member  29  of the insertion support tool  4  is fitted in the locking concave portion  52  of the outer cylindrical portion  20   b  of the end unit  16 , thereby forming a concavoconvex fitting portion  54 . This concavoconvex fitting portion  54  forms engagement means for holding the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 .  
      A function of this embodiment having the above-mentioned structure will now be described. In this embodiment, the insertion support tool  4  is maintained in a state where an external sheath  14  is previously contracted before use and the hard cover member  29  is arranged on the outer side of the external sheath  14  to cover the external sheath  14 . At this time, the engagement protrusion  51  of the cover member  29  of the insertion support tool  4  moves over the rear end flange portion  53  of the outer cylindrical portion  20   b  of the end unit  16  to be fitted in the locking concave portion  52 , thereby forming the concavoconvex fitting portion  54 . This concavoconvex fitting portion  54  maintains an engagement state in which the end portion of the cover member  29  is releasably engaged with the end unit  16 . In this state, there are carried out an operation of attaching the insertion support tool  4  to the inserting portion  3  of the large-intestine endoscope  2  (an insertion support tool attachment step) and an operation of inserting an assembled unit  33  having the insertion support tool  4  assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  into a large intestine (a rectum) H 2  from the anus H 1  of a patient H (a first insertion step).  
      Furthermore, in regard to engagement strength of the concavoconvex fitting portion  54  between the engagement protrusion  51  of the cover member  29  and the locking concave portion  52  of the outer cylindrical portion  20   b  of the end unit  16 , it is preferable to set a working fluid such as pressurized air from a fluid path  26  to a pressure of air or below supplied to a part between an outer sheath  18  and an inner sheath  19  of the external sheath  14 . In this case, start of an extending operation of the external sheath  14  by supply of the working fluid such as pressurized air from the fluid path  26  releases engagement between the end portion of the cover member  29  and the end unit  16 .  
      Thereafter, supplying the working fluid such as pressurized air to the space between the outer sheath  18  and the inner sheath  19  of the external sheath  14  can extend the entire external sheath  14  in an inserting direction of the inserting portion  3  of the large-intestine endoscope  2 . As a result, the insertion support tool  4  can move forward in a state where the end unit  16  is pushed forward with respect to a base unit  15 . At this time, the inserting portion  3  of the large-intestine endoscope  2  is moved forward together with the end unit  16  in the inserting direction of the inserting portion  3  (a second insertion step).  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope insertion apparatus  1  according to this embodiment, the engagement protrusion  51  of the cover member  29  of the insertion support tool  4  moves over the rear end flange portion  53  of the outer cylindrical portion  20   b  of the end unit  16  to be fitted in the locking concave portion  52 , whereby the end portion of the cover member  29  can be engaged with the end unit  16 . Therefore, it is possible to readily carry out the engagement operation of holding the end portion of the cover member  29  in a state where this end portion is in contact with the first flange portion  23  of the end unit  16 .  
       FIG. 11  shows a fourth embodiment according to the present invention. This embodiment can be obtained by changing the configuration of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, a barb portion  61  having a diameter larger than that of any part other than an end portion of a cover member  29  is provided at the end portion of the cover member  29  of an insertion support tool  4 . This barb portion  61  is obtained by smoothing the end portion of the cover member  29  and increasing a diameter of the same. A bent portion  62  which is bent in a direction substantially orthogonal to an axial direction of the insertion support tool  4  is formed at a base end portion of this barb portion  61 .  
      A function of the above-mentioned configuration will now be described. In this embodiment, at the time of an operation of inserting an assembled unit  33  having the insertion support tool  4  assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (rectum) H 2  from the anus H 1  of a patient H (a first insertion step), the assembled unit  33  is pushed in until the barb portion  61  of the cover member  29  moves over the anus H 1  of the patient H. At this time, when the barb portion  61  of the cover member  29  moves past the anus H 1  of the patient H, the force needed is suddenly reduced. Therefore, at the time of the operation of inserting the assembled unit  33  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H, it is possible to relatively easily confirm, from an operational feeling of an operator, when the barb portion  61  of the cover member  29  moves past the anus H 1  of the patient H by a change in the force needed for pushing in the assembled unit  33 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effect. That is, in the endoscope insertion apparatus  1  according to this embodiment, it is possible to confirm from an operational feeling of an operator when the barb portion  61  of the cover member  29  moves past the anus H 1  of the patient H during the operation of inserting the assembled unit  33  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H. Therefore, since the insertion support tool  4  can be assuredly inserted to a correct insertion position, it is possible to further readily perform the operation of inserting the assembled unit  33  having the insertion support tool  4  assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H (the first insertion step).  
      Moreover, when the insertion support tool  4  has been inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H, as shown in  FIG. 11 , a step portion between the bent portion  62  of the barb portion  61  and the outer peripheral surface of the cover member  29  can be brought into contact with a wall surface between the inside of the large intestine (the rectum) H 2  and the anus H 1 . Therefore, the insertion support tool  4  which has been inserted into the large intestine (the rectum) H 2  can be prevented from being easily pulled out from the large intestine (the rectum) H 2  during the operation of inserting the inserting portion  3  of the large-intestine endoscope  2 .  
       FIGS. 12 and 13  show a fifth embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  of the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, there is provided a protection member  71  which is previously inserted into the large intestine (rectum) H 2  from the anus H 1  of a patient H and attached in a muzzle-loaded state before inserting a main body of an insertion support tool  4  as shown in  FIG. 12 . This protection member  71  has a cylindrical member  72  formed of a hard material and a large-diameter mouthpiece member  73  formed of a resin which is coupled with a base end portion of this cylindrical member  72 .  
      As shown in  FIG. 13 , in the mouthpiece member  73 , a mouthpiece engagement groove  74  as a fixing portion at which at least a part of the insertion support tool  4  is fixed is formed on a circumferential wall surface of the mouthpiece member  73  on a base end portion side thereof. This mouthpiece engagement groove  74  is formed into a shape which can be engaged with an air supply mouthpiece  27  of a mouthpiece member  17  of the insertion support tool  4 .  
      An engagement protrusion  75  which protrudes toward an inner side of the mouthpiece engagement groove  74  is formed on each of both sides of an opening end portion (a left end portion in  FIG. 13 ) of the mouthpiece engagement groove  74 . A narrow-width portion  76  whose width is narrower than a groove width of the mouthpiece engagement groove  74  is formed between the engagement protrusions  75  on both sides.  
      Further, when an endoscope insertion apparatus  1  according to this embodiment is used, an assembled unit  33  having the insertion support tool  4  assembled at an end portion of an inserting portion  3  of a large-intestine endoscope  2  according to the first embodiment is inserted into the protection member  71 .  
      A function of this embodiment having the above-mentioned configuration will now be described. In this embodiment, when the large-intestine endoscope  2  is used, the cylindrical member  72  of the protection member  71  is previously inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H and attached in a muzzle-loaded state. Then, the assembled unit  33  having the insertion support tool  4  assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  according to the first embodiment is inserted into the protection member  71 . When inserting this insertion support tool  4 , as indicated by an arrow in  FIG. 13 , the air supply mouthpiece  27  of the mouthpiece member  17  covers the narrow-width portion  76  from the opening end portion of the mouthpiece engagement groove  74  to be engaged with the mouthpiece engagement groove  74 . As a result, the insertion support tool  4  can be prevented from rotating in a periaxial direction or from coming off with respect to the protection member  71 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope insertion apparatus  1  according to this embodiment, the protection member  71  is provided separately from the insertion support tool  4 , and the cylindrical member  72  of the protection member  71  is previously inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H and attached in a muzzle-loaded state before inserting the main body of the insertion support tool  4 . Therefore, the main body of the insertion support tool  4  can be protected by this protection member  71  in the muzzle-loaded state, thereby reducing a length of the cover member  29  of the insertion support tool  4 . As a result, the insertion support tool  4  can be relatively reduced in dimension and configured to be compact, thus improving handling properties or attachment properties with respect to the large-intestine endoscope  2 .  
      Furthermore, since the main body of the insertion support tool  4  can be inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H by just performing the simple operation of inserting the main body of the insertion support tool  4  into the cylindrical member  72  of the protection member  71 , it is possible to readily effect the operation of inserting the insertion support tool  4  into the large intestine (the rectum) H 2  from the anus H 1  of the patient H.  
      FIGS.  14  to  16  show a sixth embodiment according to the present invention. This embodiment is obtained by changing the configuration of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, a packing material  81  which is used to pack an insertion support tool  4  is provided as shown in  FIG. 15 . This packing material  81  has a pedestal unit  82  shown in  FIG. 14  and a packing bag  83  depicted in  FIG. 15 . The pedestal unit  82  has a tabular pedestal  84 , and a pair of (first and second) support leg portions  85  and  86  standing on this pedestal  84 . A substantially U-shaped first engagement groove  85   a  is formed in the first support leg portion  85 . Likewise, a substantially U-shaped engagement groove  86   a  is formed in the second support leg portion  86 .  
      Moreover, in the insertion support tool  4  according to this embodiment, a first annular groove  87  is formed on an outer peripheral surface of a mouthpiece member  17  of a base unit  15  and a second annular groove  88  is formed on an outer peripheral surface of an end member  21  of an end unit  16 , respectively. The first annular groove  87  of the mouthpiece member  17  is releasably engaged in the first engagement groove  85   a  of the first support leg portion  85  on the pedestal  84  and the second annular groove  88  of the end member  21  is releasably engaged in the second engagement groove  86   a  of the second support leg portion  86  on the same, respectively. Additionally, the insertion support tool  4  on the pedestal  84  is restricted to a fixed set length between front and rear parts thereof and a fixed shape by engagement of the first and second support leg portions  85  and  86 . As a result, an external sheath  14  is contracted and held in a state where a cover member  29  covers the external sheath  14 .  
      A packing bag  83  is formed of a sterile bag in which an entire assembled unit including the pedestal unit  82  and the insertion support tool  4  is accommodated in a state where the insertion support tool  4  is held on the pedestal  84 . An unsealing portion  89  is formed at one end portion of this packing bag  83 . Further, the insertion support tool  4  is accommodated in a state where the mouthpiece member  17  of the base unit  15  is arranged on the unsealing portion  89  side.  
      A function of this embodiment having the above-mentioned configuration will now be described. In the endoscope insertion apparatus  1  according to this embodiment, there is carried out an operation of assembling an end portion of an inserting portion  3  of a large-intestine endoscope  2  with respect to the insertion support tool  4  in a state where the entire assembled unit including the pedestal unit  82  and the insertion support tool  4  is accommodated in the packing bag  83 . At the time of this operation, as shown in  FIG. 16 , the unsealing portion  89  of the packing bag  83  is opened. At this time, the mouthpiece member  17  of the insertion support tool  4  is exposed from the unsealing portion  89  of the opened packing bag  83 . Therefore, the end portion of the inserting portion  3  of the large-intestine endoscope  2  can be inserted from the mouthpiece member  17  of the insertion support tool  4  in a state where the insertion support tool  4  is within the packing bag  83 . At this time, since the insertion support tool  4  is fixed on the pedestal  84 , the insertion support tool  4  is not moved. Therefore, an operator can insert the end portion of the inserting portion  3  of the large-intestine endoscope  2  from the mouthpiece member  17  of the insertion support tool  4  through the packing bag  83  and then assemble the end portion of the inserting portion  3  of the large-intestine endoscope  2  with respect to the insertion support tool  4  without directly touching the insertion support tool  4 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, the packing material  81  which is used to pack the insertion support tool  4  is provided, and the packing bag  83  is formed of a sterile bag which accommodates the entire assembled unit including the pedestal unit  82  and the insertion support tool  4  in a state where the insertion support tool  4  is held on the pedestal  84 . The insertion support tool  4  on the pedestal  84  is restricted to a fixed set length between the front and rear sides and a shape by engagement between the first and second support leg portions  85  and  86 . As a result, the insertion support tool  4  is held in a state where the external sheath  14  is contracted and the cover member  29  covers the external sheath  14 , and hence the external sheath  14  of the insertion support tool  4  can be prevented from being extended during transport. Therefore, an inconvenience of the insertion support tool  4  before use can be avoided.  
      Further, an operator can perform an operation of assembling the end portion of the inserting portion  3  of the large-intestine endoscope  2  with respect to the insertion support tool  4  through the packing bag  83  without directly touching the insertion support tool  4  with his/her hand. As a result, the external sheath  14  can be prevented from being extended or attached at the time of taking out or attaching the insertion support tool  4 , thereby improving the handling properties of the insertion support tool  4 . Therefore, it is possible to improve the workability of the assembling operation of assembling the end portion of the inserting portion  3  of the large-intestine endoscope  2  with respect to the insertion support tool  4 .  
       FIG. 17  shows a first modification of the packing bag  83  of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the sixth embodiment (see FIGS.  14  to  16 ). A packing bag  91  according to this modification has a box-shaped packing bag main body  92  whose upper surface is opened and a sealing film  93  which covers the upper surface opening portion of this packing bag main body  92 .  
      Moreover, a narrow-width portion  94  is formed at a part of the packing bag main body  92 . This narrow-width portion  94  is provided at a position corresponding to a mouthpiece member  17  of an insertion support tool  4 . Additionally, a sealing portion  95  of the sealing film  93  is formed on an entire circumference of the packing bag main body  92  at a rim portion of the upper surface opening portion. An unsealing portion  96  having a weak sealing force is provided at a part of this sealing portion  95 . This unsealing portion  96  is arranged at the narrow-width portion  94  of the packing bag main body  92 . It is to be noted that an indicating portion  97  such as a label indicating a product name or the like of the insertion support tool  4  accommodated in the packing bag main body  92  is provided in a vacant space of a pedestal  84  of the insertion support tool  4 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this modification, a mouthpiece member  17  of the insertion support tool  4  can be exposed by unsticking the sealing film  93  from the unsealing portion  96  at the narrow-width portion  94  of the packing bag main body  92 . Therefore, an end portion of an inserting portion  93  of a large-intestine endoscope  2  can be inserted from the mouthpiece member  17  of the insertion support tool  4  in a state where the insertion support tool  4  is within the packing bag  83 . At this time, since the pedestal  84  of the insertion support tool  4  has a large width, a pressing action can be facilitated during an operation of inserting the end portion of the inserting portion  3  of the large-intestine endoscope  2 .  
      Additionally, in this modification, since any part of the insertion support tool  4  other than the mouthpiece member  17  in the packing bag main body  92  is not exposed, storage until use can be facilitated, thus reducing a risk such as contamination.  
       FIG. 18  shows a second modification of the packing bag  83  of the insertion support tool  4  according to the sixth embodiment (see FIGS.  14  to  16 ). In a packing bag  101  according to this modification, narrow-width portions  94  are formed at both end portions of the packing bag main body  92  of the packing bag  91  according to the first modification (see  FIG. 17 ).  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the packing bag  101  according to this modification, like the packing bag  91  according to the first modification, an end portion of an inserting portion  3  of a large-intestine endoscope  2  is assembled with respect to an insertion support tool  4  in the packing bag main body  92 , and then an end side of the insertion support tool  4  is exposed, thereby holding and fixing the inserting portion  3  of the large-intestine endoscope  2 . Therefore, the inserting portion  3  of the large-intestine endoscope  2  can be assuredly held and fixed.  
       FIG. 19  shows a third modification of the packing bag  83  of the insertion support tool  4  according to the sixth embodiment (see FIGS.  14  to  16 ). In a packing bag  111  according to this modification, an upper side of the pedestal unit  82  according to the sixth embodiment is covered with a sealing film  93 , and a sealing portion  112  obtained by welding and fixing a rim part of the sealing film  93  is provided at an outer peripheral part of a pedestal  84 . Moreover, the packing bag  111  according to this modification has an effect of facilitating recycling.  
      It is to be noted that the pedestal  84  and first and second support leg portions  85  and  85  provided thereon may be integrally molded by using, e.g., cardboard in the packing bag  111  according to this modification. Additionally, the sealing film  93  may be formed of a transparent film. In this case, there is an effect that the contents of the packing bag  11  can be directly seen through the transparent sealing film  93 .  
       FIGS. 20A and 20B  shows a fourth modification of the packing bag  83  of the insertion support tool  4  according to the sixth embodiment (see FIGS.  14  to  16 ). In a packing bag  121  according to this modification, an insertion support tool  4  is accommodated in a concave portion  123  of a blister packing  122  formed of a transparent resin material as shown in  FIG. 20B . Furthermore, a flange portion  124  is formed at a rim part of the concave portion  123  of the blister packing  122 . A rim part of a sealing sheet  125  which closes an upper surface opening portion of the concave portion  123  of the blister packing  122  is attached on this flange portion  124 .  
      A dimension of the concave portion  123  of the blister packing  122  is substantially the same as that of the insertion support tool  4 . Moreover, it is preferable for the concave portion  123  of the blister packing  122  to have a depth which allows accommodation of the entire insertion support tool  4 . Additionally, a peeling start portion  126  which facilitates peeling from the flange portion  124  of the blister packing  122  is formed on one end portion side of the sealing sheet  125 . An indicating portion  127  which indicates a position at which a mouthpiece member  17  of the insertion support tool  4  is exposed is provided to this peeling start portion  126 .  
      Further, in the packing bag  121  according to this modification, since the blister packing  122  is transparent, the insertion support tool  4  accommodated in the concave portion  123  can be visually observed. Furthermore, at the point of use, the mouthpiece member  17  of the insertion support tool  4  alone can be exposed by peeling the peeling start portion  126  on one end portion side of the sealing sheet  125 . Therefore, there is an effect that the apparatus is hardly contaminated.  
      Moreover, since the packing bag  121  according to this modification is configured to accommodate the entire insertion support tool  4  in the concave portion  123  of the blister packing  122 , a shape of the insertion support tool  4  can be held, and takeoff can be facilitated.  
      Additionally, since the indicating portion  127  indicating a position as a guide for exposure of the mouthpiece member  17  of the insertion support tool  4  is provided on one end portion side of the sealing sheet  125 , the sealing sheet  125  is not unnecessarily greatly peeled off. Therefore, a risk of contamination is small.  
       FIGS. 21A and 21B  show a fifth modification of the packing bag  93  of the insertion support tool  4  according to the sixth embodiment (see FIGS.  14  to  16 ). A packing bag  131  according to this modification is obtained by changing the packing bag  121  according to the fourth modification (see  FIGS. 20A and 20B ) as follows.  
      That is, in the packing bag  131  according to this modification, as shown in  FIG. 21A , a thin-walled portion  132  is formed at one end portion of a concave portion  123  of a blister packing  122 . Furthermore, as shown in  FIG. 21B , like the packing bag  121  according to the fourth modification, a mouthpiece member  17  of an insertion support tool  4  alone is exposed by peeling a peeling start portion  126  provided on one end portion side of a sealing sheet  125 , and the thin-walled portion  132  is held and pushed in this state. As a result, the mouthpiece member  17  of the insertion support tool  4  is exposed to the outside from an upper surface opening portion of the concave portion  123  of the blister packing  122 . Therefore, an operation of inserting an end portion of an inserting portion  3  of a large-intestine endoscope  2  into the mouthpiece member  17  of the insertion support tool  4  can be facilitated.  
      FIGS.  22  to  27 B show a seventh embodiment according to the present invention. This embodiment is obtained by changing the configuration of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the first embodiment (see FIGS.  1  to  7 A) as follows. It is to be noted that, in FIGS.  22  to  27 B, like reference numerals denote parts equal to those depicted in FIGS.  1  to  7 A, thereby obviating their explanation.  
      As shown in  FIG. 23 , an end member  21  of an end unit  16  of an insertion support tool  4  according to this embodiment has an endoscope attachment portion  141 , an end opening portion  142  for suction, and an air supply/water supply nozzle  143 . As shown in  FIG. 24 , an end portion of a suction tube  145  is coupled with the end opening portion  142 . An end portion of an air supply/water supply tube  144  is coupled with the air supply/water supply nozzle  143 . The air supply/water supply nozzle  143  is fixed in a state where it emits a fluid toward a cover glass  32  of the endoscope attachment portion  141 . Additionally, a key groove  152  is formed at a part of an endoscope attachment hole  31  of the end member  21  in a circumferential direction. This key groove  152  is extended in an inserting direction of an inserting portion  3  of a large-intestine endoscope  2 .  
      Further, as shown in  FIG. 25 , a key  153  which is releasably engaged with the key groove  152  is provided to protrude from an end hard portion  8  of the large-intestine endoscope  2 . Furthermore, a rubber ring  154  is attached on an outer peripheral surface of the end hard portion  8 . Moreover, at the time of an operation of attaching the insertion support tool  4  with respect to the inserting portion  3  of the large-intestine endoscope  2 , the key  153  of the end hard portion  8  and the key groove  152  of the end member  21  are positioned and engaged. As a result, when the insertion support tool  4  is attached to the inserting portion  3  of the large-intestine endoscope  2 , the end hard portion  8  can be positioned in the circumferential direction in the endoscope attachment hole  31  of the end member  21  by engagement established between the key  153  of the end hard portion  8  and the key groove  152  of the end member  21 . Therefore, as shown in  FIG. 23 , a spouting fluid (washing water) from the air supply/water supply nozzle  143  can be appropriately emitted toward an observation window  9  of the end hard portion  8 . Additionally, when the end hard portion  8  is inserted into the endoscope attachment hole  31  of the end member  21 , the end hard portion  8  is fastened and fitted in the endoscope attachment hole  31  of the end member  21  by the rubber ring  154  of the end hard portion  8  so that engagement between both the members cannot be released.  
      Further, as shown in  FIG. 26 , a tabular support member  146  which partitions a rear end opening portion in the vertical direction is arranged on a mouthpiece member  17  of the insertion support tool  4 . In  FIG. 26 , a first interior space  146   a  is formed on an upper side of this support member  146  and a second interior space  146   b  is formed on a lower side of the same, respectively. Furthermore, the suction tube  145  and the air supply/water supply tube  144  are inserted into the first interior space  146   a . The inserting portion  3  of the large-intestine endoscope  2  is inserted into the second interior space  146   b.    
      Moreover, a circumferential wall portion on the second interior space  146   b  side has an endoscope pressing portion  147 . This endoscope pressing portion  147  has an operation button  148  as shown in  FIG. 27B . An outer end portion of this operation button  148  protrudes toward the outside of the mouthpiece member  17 . Additionally, a shaft portion  148   a  of the operation button  148  protrudes toward the inside of the mouthpiece member  17 . A pushing member  149  is fixed at an inner end portion of this shaft portion  148   a . As shown in  FIG. 27A , this pushing member  149  is formed into an arc shape corresponding to a flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2 . Further, a nonslip member  150  formed of a rubber member is fixed on an inner surface of the pushing member  149 .  
      Furthermore, a return spring  151  formed of a coil spring is attached to the shaft portion  148   a  of the operation button  148 . This return spring  151  gives an impetus to the operation button  148  in a direction along which this button protrudes toward the outside of the mouthpiece member  17 . Moreover, as indicated by an arrow in  FIG. 27B , pushing the operation button  148  against the impetus of the return spring  151  causes the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2  to be held between the pushing member  149  and the support member  146 , thereby generating a frictional force. As a result, the inserting portion  3  of the large-intestine endoscope  2  can be releasably engaged with and fixed to the base unit  15 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, the inserting portion  3  of the large-intestine endoscope  2  can be moved back by pulling the base unit  15  of the insertions support tool  4  toward the front side (a direction opposite to the inserting direction of the inserting portion  3  of the large-intestine endoscope  2 ) while pushing the operation button  148  against the impetus of the return spring  151 . At this time, the inserting portion  3  of the large-intestine endoscope  2  can be moved back in a state where a length between the base unit  15  of the insertion support tool  4  and the end member  21  is fixed. Therefore, during the operation of moving back the inserting portion  3  of the large-intestine endoscope  2 , an outer sheath  18  and an inner sheath  19  of the insertion support tool  4  are not folded in a disorderly manner, or an already folded part is not unfolded.  
      Additionally, the mouthpiece member  17  of the insertion support tool  4  is partitioned into the first interior space  146   a  and the second interior space  146   b  by the tabular support member  146 . Further, since the suction tube  145  and the air supply/water supply tube  144  are inserted into the first interior space  146   a  and the inserting portion  3  of the large-intestine endoscope  2  is inserted into the second interior space  146   b , the suction tube  145  or the air supply/water supply tube  144  in the insertion support tool  4  is protected by the support member  146 . As a result, the suction tube  145  or the air supply/water supply tube  144  in the insertion support tool  4  is not damaged during the operation of moving back the inserting portion  3  of the large-intestine endoscope  2 .  
      The endoscope pressing portion  147  according to this embodiment has a configuration in which a force of pushing the operation button  148  is directly transmitted as a pushing force of the inserting portion  3  of the large-intestine endoscope  2 , i.e., a locking force when locking with the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2  being held between the pushing member  149  and the support member  146 . Therefore, a large frictional force can be generated with a compact mechanism.  
      Furthermore, since the nonslip member  150  formed of the rubber member is fixed on the inner surface of the pushing member  149 , a large frictional force can be generated, and it is possible to perform an assured operation of locking with the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2  being held. Here, as shown in  FIG. 27A , since the pushing member  149  is formed into the arc shape corresponding to the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2 , thus generating a larger frictional force.  
       FIGS. 28 and 29  show a first modification of the endoscope pressing portion  147  of the insertion support tool  4  of the endoscope insertion portion  1  according to the seventh embodiment (see FIGS.  22  to  27 B). In an endoscope pressing portion  161  according to this modification, a return spring  151  of a shaft portion  148   a  of an operation button  148  is provided in a state where an impetus functions in a direction along which a pushing member  149  is pushed toward the inside of a mouthpiece member  17 . It is to be noted that  FIG. 28  shows a state where the operation button  148  is pushed and  FIG. 29  shows a state where pushing of the operation button  148  is released.  
      Additionally, one end portion of an operation lever  162  which releases a locked state of an inserting portion  3  of a large-intestine endoscope  2  by the endoscope pressing portion  161  is coupled with a head portion of the operation button  148  in such a manner that this end portion can swivel. As shown in  FIG. 29 , when this operation lever  162  is moved down toward a protruding receiving portion (a supporting point)  163  side of a mouthpiece member  17 , the pushing member  149  is moved away from a flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2 . As a result, the inserting portion  3  of the large-intestine endoscope  2  can move forward and backward.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, the endoscope pressing portion  161  according to this modification has a configuration in which the pushing member  149  is moved away from the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2  when the operation lever  162  is moved down toward the protruding receiving portion  163  side of the mouthpiece member  17 . Therefore, when the mouthpiece member  17  is grasped by hand, it is possible to avoid a pushing operation of the operation button  148  which causes the endoscope pressing portion  161  to operate.  
      Further,  FIG. 30A  shows a second modification of the endoscope pressing portion  147  of the insertion support tool  4  according to the seventh embodiment (see FIGS.  22  to  27 B). In an endoscope pressing portion  171  according to this modification, a support member  146  of a mouthpiece member  17  is curved along an outer shape of an inserting portion  3  of a large-intestine endoscope  2  and a nonslip  172  formed of a rubber member is provided on an inner peripheral surface of the support member  146  having the curved shape.  
      Accordingly, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope pressing portion  171  according to this modification, a contact area of the support member  146  having the curved shape and the inserting portion  3  of the large-intestine endoscope  2  is large, and hence a large frictional force can be obtained.  
      Furthermore,  FIG. 30B  shows a third modification of the endoscope pressing portion  147  of the insertion support tool  4  according to the seventh embodiment (see FIGS.  22  to  27 B). In an endoscope pressing portion  181  according to this modification, a support member  146  of a mouthpiece member  17  is formed of a material having hardness which allows appropriate transformation. Here, the hardness of the support member  146  which allows appropriate transformation is a hardness which allows transformation without damaging a suction tube  145  or an air supply/water supply tube  144  in a first interior space  146   a  when an operation button  148  is pushed and a pushing member  149  thereby pushes a flexible tube portion  6  of an inserting portion  3  of a large-intestine endoscope  2 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope pressing portion  181  according to this modification, when the operation button  148  is pushed, the support member  146  appropriately transforms in accordance with an outer shape of the inserting portion  3  of the large-intestine endoscope  2 . Therefore, a contact area of a transformed portion  182  having a curved shape of the support member  146  and the inserting portion  3  of the large-intestine endoscope  2  is large, thereby obtaining a large frictional force.  
       FIGS. 31A and 31B  show an eighth embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope pressing portion  147  of the inserting support tool  4  according to the seventh embodiment (see FIGS.  22  to  27 B) as follows.  
      That is, in an endoscope pressing portion  191  according to this embodiment, an inflatable balloon  192  is provided in place of the pushing member  149  of the operation button  148  according to the seventh embodiment as shown in  FIG. 31A . One end portion of an air supply tube  193  is connected with this balloon  192 . The other end portion of this air supply tube  193  is connected with an air supply source of a non-illustrated compressor or the like. Further, when air or the like is supplied into the balloon  192 , as shown in  FIG. 31B , the balloon  192  inflates. At this time, a flexible tube portion  6  of an inserting portion  3  of a large-intestine endoscope  2  is held and locked between the balloon  192  and a support member  146 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope pressing portion  191  according to this embodiment, since the balloon  192  is provided in place of the pushing member  149  of the operation button  148  according to the seventh embodiment, the configuration is compact and a weight is reduced. Therefore, the entire insertion support tool  4  can be reduced in size and weight, thereby lessening fatigue during endoscopy.  
       FIG. 32  shows a ninth embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope pressing portion  147  of the insertion support tool  4  of the seventh embodiment (see FIGS.  22  to  27 B) as follows.  
      That is, in an endoscope pressing portion  201  according to this embodiment, a donut-like balloon  202  is provided in place of the balloon  192  according to the eighth embodiment (see  FIGS. 31A and 31B ). One end portion of an air supply tube  203  is connected with this balloon  202 . The other end portion of this air supply tube  203  is connected with an air supply source of a non-illustrated compressor or the like. Moreover, when air or the like is supplied into the balloon  202 , the balloon  202  inflates as indicated by dotted lines in  FIG. 32 . At this time, a flexible tube portion  6  of an inserting portion  3  of a large-intestine endoscope  2  is compressed and locked from an entire circumference of the balloon  202 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope pressing portion  201  according to this embodiment, since the donut-like balloon  202  is provided, the flexible tube portion  6  of the inserting portion  3  of the large-intestine endoscope  2  can be compressed and locked from the entire circumference of the balloon  202 . Therefore, a large frictional force can be obtained.  
       FIG. 33  shows a 10th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope pressing portion  147  of the insertion support tool  4  of the seventh embodiment (see FIGS.  22  to  27 B) as follows.  
      That is, in this embodiment, for example, a driving switch  211  of a compressor (or a switch of a valve which controls air from the compressor) which supplies a fluid to an external sheath  14  of an insertion support tool  4  is provided at a position of the receiving portion (a supporting point)  163  of the operation lever  162  in the endoscope pressing portion  161  according to the first modification (see  FIGS. 28 and 29 ) of the seventh embodiment.  
      Further, in this embodiment, when an operation lever  162  of an endoscope pressing portion  161  is moved down toward a receiving portion  163  side, a locked state of a pushing member  149  of an operation button  148  is released and, at the same time, the driving switch  211  is turned on, thereby supplying a fluid to the external sheath  14 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, two operations, i.e., releasing the locked state of the pushing member  149  of the operation button  148  and supplying a fluid to the external sheath  14  can be performed by one operation of moving down the operation lever  162  of the endoscope pressing portion  161  toward the receiving portion  163  side.  
       FIG. 34  shows an 11th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  of the seventh embodiment (see FIGS.  22  to  27 B) as follows.  
      That is, in this embodiment, a lateral cross-sectional shape of an inserting portion  3  of a large-intestine endoscope  2  is formed into an elliptic shape. Moreover, a lateral cross-sectional shape of a second interior space  146   b  of a support member  146  is formed into an elliptic shape corresponding to the elliptic shape of the inserting portion  3  of the large-intestine endoscope  2 . As a result, when the inserting portion  3  of the large-intestine endoscope  2  or a mouthpiece member  17  of the insertion support tool  4  is twisted in a periaxial direction with the inserting portion  3  of the large-intestine endoscope  2  being inserted in the second interior space  146   b , both the inserting portion  3  of the large-intestine endoscope  2  and the insertion support tool  4  can be prevented from being freely rotated.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, when the inserting portion  3  of the large-intestine endoscope  2  or the mouthpiece member  17  of the insertion support tool  4  is twisted in the periaxial direction, follow-up properties with respect to rotation are good, and a treatment can be excellently performed.  
       FIGS. 35A  to  35 E show a 12th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the primary part of the insertion support tool  4  of the endoscope insertion apparatus  1  of the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, as shown in  FIG. 35A , a flange portion  211  is provided at a rear end surface of a mouthpiece member  17  of an insertion support tool  4 . As depicted in  FIG. 35B , this flange portion  211  is integrally formed with the mouthpiece member  17 . Further, as shown in  FIG. 35C , when the insertion support tool  4  is inserted into an anus, the flange portion  211  of the mouthpiece member  17  is fixed on a body wall such as the buttocks of a patient by an adhesive tape  212  or the like.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, when the insertion support tool  4  is inserted into the anus, the flange portion  211  of the mouthpiece member  17  can be fixed on the body wall such as buttocks of a patient by the adhesive tape  212  or the like. Therefore, for example, as shown in  FIG. 35D , when an extending force is applied to a rear side rather than a front side in a state where an end of the insertion support tool  4  is in contact with a bent part in a large intestine H 2 , the insertion support tool  4  can be prevented from coming out of the anus. On the contrary, for example, in a case where the insertion support tool  4  is pulled into the anus when the patient moves, movement of the insertion support tool  4  can be suppressed. As a result, an operator or a helper does not have to hold the mouthpiece member  17  during the operation of the insertion support tool  4 , thereby making the task less strenuous.  
       FIGS. 36A and 36B  show a modification of the flange portion  211  of the insertion support tool  4  of the endoscope insertion apparatus  1  according to the 12th embodiment (see  FIGS. 35A  to  35 E). In this modification, a flange attachment groove  221  is provided on an outer peripheral surface of a rear end portion of a mouthpiece member  17  of an insertion support tool  4  as shown in  FIG. 36A . A flange constituent member  222 , which is different from the mouthpiece member  17 , is detachably attached in this flange attachment groove  221 . As depicted in  FIG. 36B , this flange constituent member  222  is formed of an elastic member, and a circular fitting hole  222   a  is formed at an axial center portion thereof. Furthermore, the fitting hole  222   a  can be fitted on the flange attachment groove  221  of the mouthpiece member  17  by elastically deforming the flange constituent member  222 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this modification, since the flange constituent member  222  is detachably attached in the flange attachment groove  221  of the mouthpiece member  17 , the flange constituent member  222  can be readily taken out from the flange attachment groove  221  of the mouthpiece member  17  when it is unnecessary. Therefore, the flange constituent member  222  of the mouthpiece member  17  is not an obstacle at the time of transport or disposal.  
       FIG. 37  shows an insertion support tool  4  according to a 13th embodiment of the present invention. This embodiment is obtained by changing the configuration of the primary part of the insertion support tool  4  in the endoscope insertion apparatus  1  of the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, an air supply mouthpiece  27  of a mouthpiece member  17  of an insertion support tool  4  is extended long in a lateral direction. Moreover, when the insertion support tool  4  is inserted into an anus, the air supply mouthpiece  27  is fixed on a body wall such as the buttocks of a patient by an adhesive tape  231 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, the air supply mouthpiece  27  can be used in place of the flange portion  211  of the insertion support tool  4  according to the 12th embodiment (see  FIGS. 35A  to  35 E). Therefore, the number of components is not increased, which is efficient.  
       FIGS. 38A and 38B  show an insertion support tool  4  according to a 14th embodiment of the present invention. This embodiment is obtained by changing the configuration of the primary part of the insertion support tool  4  in the endoscope insertion apparatus  1  of the first embodiment (see FIGS.  1  to  7 A) as follows.  
      That is, in this embodiment, a belt winding groove  241  is provided on an outer peripheral surface of a mouthpiece member  17  of an insertion support tool  4 . Additionally, when the insertion support tool  4  is inserted into an anus, as shown in  FIG. 38A , the insertion support tool  4  is fixed to a patient H by winding a fixing belt  242  between the belt winding groove  241  of the mouthpiece member  17  and a leg of a patient H. As the fixing belt  242 , it is possible to use a buckle type belt, a Velcro strap (a registered trademark), a rubber band and others.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, since the fixing belt  242  is wound between the belt winding groove  241  of the mouthpiece member  17  and the leg of the patient H, fixation of the insertion support tool  4  is assured.  
      FIGS.  39  to  41 C show a 15th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the primary part of the insertion support tool  4  in the endoscope insertion apparatus  1  of the first embodiment (see FIGS.  1  to  7 A) as follows.  
      As shown in  FIG. 39 , an insertion support tool  4  according to this embodiment has an endoscope attachment hole  31  and a forceps channel  251  in an end member  21 . Furthermore, as shown in  FIG. 40 , a positioning index  252  for positioning with a mouthpiece member  17  of a base unit  15  is provided to an inserting portion  3  of a large-intestine endoscope  2 .  
      A function of the above-mentioned configuration will now be described. In this embodiment, at the time of an operation of assembling the insertion support tool  4  to an end portion of the inserting portion  3  of the large-intestine endoscope  2 , the positioning index  252  of the insertion portion  3  of the large-intestine endoscope  2  is positioned with the mouthpiece member  17  of the base unit  15 . As a result, the insertion support tool  4  can be assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2  in a state where a rotating position of the inserting portion  3  of the large-intestine endoscope  2  in a periaxial direction is correctly positioned with respect to the insertion support tool  4 . Therefore, a position of the forceps channel  251  with respect to an observation image of the large-intestine endoscope  2  can be set to a fixed relationship. As a result, a direction along which an instrument appears in an observation image of the large-intestine endoscope  2  can be fixed.  
      It is to be noted that  FIGS. 41A  to  41 C show display states of an instrument  255  in an observation image of the large-intestine endoscope  2 . For example,  FIG. 41A  shows a state where the instrument  255  appears from a lower side of a screen  254 ,  FIG. 41B  shows a state where the instrument  255  appears from an upper side of the screen  254 , and  FIG. 41C  shows a state where the instrument  255  appears from a left side of the screen  254 , respectively.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, at the time of an operation of assembling the insertion support tool  4  at the end portion of the inserting portion  3  of the large-intestine endoscope  2 , the positioning index  252  of the inserting portion  3  of the large-intestine endoscope  2  is positioned with the mouthpiece member  17  of the base unit  15 . As a result, the insertion support tool  4  can be assembled with respect to the end portion of the inserting portion  3  of the large-intestine endoscope  2  in a state where a rotating position of the inserting portion  3  of the large-intestine endoscope  2  in a periaxial direction is correctly positioned with respect to the insertion support tool  4 . As a result, a display state of the instrument  255  in an observation image of the large-intestine endoscope  2  can be set to a state which facilitates an operation by a user, e.g., one of  FIGS. 41A  to  41 C. At this time, since a direction in the observation image of the large-intestine endoscope  2  along which the forceps channel  251  is arranged can be assuredly recognized, an operation of performing suction through the forceps channel  251  can be facilitated.  
       FIG. 42  shows a 16th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  of the 15th embodiment (see FIGS.  39  to  41 C) as follows.  
      That is, in this embodiment, a positioning index  256  is provided on a mouthpiece member  17  of an insertion support tool  4 . Moreover, at the time of an operation of assembling the insertion support tool  4  at an end portion of an inserting portion  3  of the large-intestine endoscope  2 , an insertion length index  257  of the inserting portion  3  of the large-intestine endoscope  2  is positioned with the positioning index  256  of the mouthpiece member  17 .  
      Thus, also in the apparatus having the above-described configuration, the insertion support tool  4  can be assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  in a state where a rotating position of the inserting portion  3  of the large-intestine endoscope  2  in a periaxial direction is correctly positioned with respect to the insertion support tool  4  like the 15th embodiment. As a result, a display state of an instrument  255  in an observation image of the large-intestine endoscope  2  can be set to a state which facilitates an operation by a user, e.g., one of  FIGS. 41A  to  41 C.  
       FIG. 43  shows a 17th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  of the 15th embodiment (see FIGS.  39  to  41 C) as follows.  
      That is, in this embodiment, a positioning index  258  is provided on a mouthpiece member  17  of an insertion support tool  4 . Additionally, a positioning index  259  is likewise provided on an inserting portion  3  of a large-intestine endoscope  2 . Further, at the time of an operation of assembling the inserting support tool  4  at an end portion of the inserting portion  3  of the large-intestine endoscope  2 , the positioning index  259  on the inserting portion  3  of the large-intestine endoscope  2  is positioned with respect to the positioning index  258  on the mouthpiece member  17 .  
      Thus, also in the apparatus having the above-described configuration, the insertion support tool  4  can be assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  in a state where a rotating position of the inserting portion  3  of the large-intestine endoscope  2  in a periaxial direction is correctly positioned with respect to the insertion support tool  4  like the 15th embodiment. As a result, a display state of an instrument  255  in an observation image of the large-intestine endoscope  2  can be set to a state which facilitates an operation by a user, e.g., one of  FIGS. 41A  to  41 C.  
       FIG. 44  shows an 18th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  according to the 17th embodiment (see  FIG. 43 ) as follows. That is, in this embodiment, a positioning index  260  linearly extended from a mouthpiece member  17  of an insertion support tool  4  to an end member  21  is provided. Furthermore, at the time of an operation of assembling the insertion support tool  4  at an end portion of an inserting portion  3  of a large-intestine endoscope  2 , a positioning index  259  on the inserting portion  3  of the large-intestine endoscope  2  is positioned with the positioning index  260  on the insertion support tool  4 .  
      Here, when distortion is generated between the mouthpiece member  17  of the insertion support tool  4  and the end member  21 , a forceps channel  251  is displaced in an observation image of the large-intestine endoscope  2  even if the positioning index  260  and the positioning index  259  on the inserting portion  3  of the large-intestine endoscope  2  are positioned at the position of the mouthpiece member  17  of the insertion support tool  4 . Thus, in the apparatus having the above-described configuration, since a positional relationship with the positioning index  259  on the inserting portion  3  of the large-intestine endoscope  2  can be confirmed at the position of the end member  21  of the insertion support tool  4 , the insertion support tool  4  can be assembled at the end portion of the inserting portion  3  of the large-intestine endoscope  2  in a state where a rotating position of the inserting portion  3  of the large-intestine endoscope  2  in a periaxial direction is correctly positioned with respect to the insertion support tool  4 . As a result, a display state of an instrument  255  in an observation image of the large-intestine endoscope  2  can be set to a state which facilitates an operation by a user, e.g., one of  FIGS. 41A  to  41 C.  
      Moreover,  FIGS. 45, 46A  and  46 B show a 19th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  according to the 17th embodiment (see  FIG. 43 ) as follows. That is, in this embodiment, a positioning index  263  linearly extended over an entire effective length of an inserting portion  3  is provided on the inserting portion  3  of a large-intestine endoscope  2 . Additionally, at the time of an operation of assembling an insertion support tool  4  at an end portion of the inserting portion  3  of the large-intestine endoscope  2 , the positioning index  263  on the inserting portion  3  of the large-intestine endoscope  2  is positioned with a positioning index  258  on the insertion support tool  4 .  
      Here, when distortion is generated between a mouthpiece member  17  of the insertion support tool  4  and an end member  21  as shown in  FIGS. 46A and 46B  during an operation of extending an external sheath  14  of the insertion support tool  4 , the external sheath  14  is crushed at a distorted part, and air used to extend the external sheath  14  is hardly supplied. Thus, in the apparatus having the above-described configuration, extending the external sheath  14  while positioning the positioning index  263  on the inserting portion  3  of the large-intestine endoscope  2  and the positioning index  258  on the insertion support tool  4  can avoid an extension defect caused due to distortion of the external sheath  14  during the operation of extending the external sheath  14 .  
       FIG. 47  shows a 20th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  according to the 18th embodiment (see  FIG. 44 ) as follows. That is, in this embodiment, a positioning index  260  linearly extended from a mouthpiece member  17  of an insertion support tool  4  to an end member  21  is provided. Furthermore, a linear positioning index  272  whose length is larger than that covered with the contracted insertion support tool  4  is provided on the inserting portion  3  of the large-intestine endoscope  2 .  
      Moreover, at the time of an operation of assembling the insertion support tool  4  at an end portion of the inserting portion  3  of the large-intestine endoscope  2 , the positioning index  260  on the insertion support tool  4  is used to confirm that an external sheath  14  is not distorted. Additionally, the positioning index  260  on the insertion support tool  4  is positioned at an end of the positioning index  272  on the inserting portion  3  of the large-intestine endoscope  2 , and insertion and attachment are performed in such a manner that a set position is not shifted.  
      Thus, in the apparatus having the above-described configuration, the insertion support tool  4  can be attached without distortion of the external sheath  14  at the time of an operation of assembling the insertion support tool  4  at the end portion of the inserting portion  3  of the large-intestine endoscope  2 . Further, during the assembling operation, this operation can be carried out without distorting the external sheath  14 .  
       FIG. 48  shows a 21st embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  1  according to the 17th embodiment (see  FIG. 43 ) as follows. That is, in this embodiment, a linear positioning index  272  whose length is larger than a length covered with a contracted insertion support tool  4  is provided on an inserting portion  3  of a large-intestine endoscope  2 .  
      Moreover, at the time of an operation of assembling the insertion support tool  4  at an end portion of the inserting portion  3  of the large-intestine endoscope  2 , a positioning index  258  on the insertion support tool  4  is positioned at an end of the positioning index  272  on the inserting portion  3  of the large-intestine endoscope  2 , and insertion and attachment are carried out in such a manner that the set position is not shifted.  
      Thus, in the apparatus having the above-described configuration, at the time of an operation of assembling the insertion support tool  4  at the end portion of the inserting portion  3  of the large-intestine endoscope  2 , this operation can be performed without distorting an external sheath  14 .  
      FIGS.  49  to  51 C show a 22nd embodiment according to the present invention.  FIG. 49  shows an endoscope insertion apparatus  301  which is an insertion support tool for a medical instrument according to this embodiment. The endoscope insertion apparatus  301  has an insertion support tool  304  which is detachably attached at an end portion of an inserting portion  303  of a large-intestine endoscope  302 .  
      The large-intestine endoscope  302  has a large-diameter operating portion at a base end portion of the elongated shaft-shaped inserting portion  303  which is inserted into a body. The inserting portion  303  has an elongated flexible tube portion  306 , a curving portion  307  which can curve in four directions, e.g., up, down, right and left directions, and an end hard portion  308 . Furthermore, a base end portion of the flexible tube portion  306  is coupled with the operating portion. An end portion of a non-illustrated curving operation wire is coupled with the curving portion  307 .  
      An end surface of the end hard portion  308  has at least one observation window and an illumination window. An objective lens is arranged behind a cover glass of the observation window. An imaging element such as a CCD is arranged at an image forming position of this objective lens. One end portion of a signal cable is connected with this imaging element. An end portion of a light guide fiber bundle is arranged behind a cover glass of the illumination window.  
      Moreover, the signal cable of the imaging element, the light guide fiber bundle, the curving operation wire and others are extended toward an operating portion side through the inside of the inserting portion  303 . Additionally, the signal cable, of the imaging element, the light guide fiber bundle, the curving operation wire and others are packed in the inserting portion  303  as built-in matters.  
      A curving operation knob which operates the curving portion  307  is arranged on the operating portion. A central shaft of the curving operation knob is coupled with a curving operation mechanism built into the operating portion. A base end portion of the curving operation wire is coupled with this curving operation mechanism. Further, the curving operation wire is towed via the curving operation mechanism by a rotating operation of the curving operation knob so that the curving portion  307  is remotely operated in an operating direction of the curving operation knob.  
      Furthermore, one end portion of a universal cord is coupled with the operating portion. A light connector and an electric signal connector are provided at the other end portion of this universal cord. The light connector is connected with a light source device and the electric signal connector is connected with a video processor, respectively. Here, the signal cable or the light guide fiber bundle is inserted into the universal cord from the operating portion. Moreover, the signal cable is connected with the electric signal connector.  
      Additionally, the other end portion of the light guide fiber bundle is connected with the light connector. Further, illumination light emitted from a light source lamp of the light source device is led to the end hard portion  308  side of the inserting portion  303  through the light guide fiber bundle, and radiated to the outside from the illumination window.  
      Furthermore, an observation image which has entered from the observation window is converted into an electric signal by the imaging element at the image forming position of the objective lens. Moreover, the electric signal is input to the video processor through the signal cable and subjected to signal processing, and then a video signal is supplied to a non-illustrated monitor so that an image is displayed in a screen of the monitor.  
      Additionally, the insertion support tool  304  has a main extension unit (a first transforming portion)  312  and an end side extension unit (a second transforming portion)  313 . The main extension unit  312  has a soft bag-shaped external sheath  314  which can be extended in an inserting direction of the inserting portion  303  of the large-intestine endoscope  302 , a base unit  315  which is coupled with a base end portion of this external sheath  314 , and an end unit  316  which is coupled with an end portion of the external sheath  314 .  
      The base unit  315  has a substantially cylindrical mouthpiece member  317 . The inserting portion  303  of the large-intestine endoscope  302  can be inserted into a cylinder of this mouthpiece member  317 . A large-diameter portion  317   a  having the largest diameter is provided on the base end portion side of the mouthpiece member  317 . An end cylindrical portion  317   b  whose diameter is smaller than that of any other part and allows insertion of the inserting portion  303  of the large-intestine endoscope  302  is provided on the end portion side of the mouthpiece member  317 . Further, an intermediate step portion  317   c  is formed between the large-diameter portion  317   a  and the end cylindrical portion  317   b  of the mouthpiece member  317 .  
      Furthermore, the external sheath  314  has an outer sheath  318  and an inner sheath  319 . A rear side fixing ring  318   a  which is fixed at the intermediate step portion  317   c  of the mouthpiece member  317  is formed at a base end portion of the outer sheath  318 . Moreover, an end side of the outer sheath  318  is extended toward the end unit  316  side. Additionally, a folded first bellows portion  318   b  is formed on this extended portion side.  
      A folded second bellows portion  319   a  is formed in the inner sheath  319 . This second bellows portion  319   a  is arranged on the end cylindrical portion  317   b  of the mouthpiece member  317 . Further, a rear side fixing ring  319   b  which is fixed at a base end portion of the end cylindrical portion  317   b  is formed at a base end portion of this second bellows portion  319   a.    
      The end unit  316  has an external sheath fixing member  320 . The external sheath fixing member  320  has an inner cylindrical portion  320   a  whose diameter is substantially the same as that of the end cylindrical portion  317   b  of the mouthpiece member  317  and an outer cylindrical portion  320   b  whose diameter is larger than that of this inner cylindrical portion  320   a . A bent portion  320   c  which is inwardly bent is formed at an end portion of the outer cylindrical portion  320   b . An inner end portion of this bent portion  320   c  is fixed on an outer peripheral surface of the inner cylindrical portion  320   a.    
      An annular flange portion  324  having a large diameter is provided to protrude from the outer peripheral surface of the inner cylindrical portion  320   a  on the base end portion side. Furthermore, an outer sheath accommodation space  325  is formed between the inner cylindrical portion  320   a  and the outer cylindrical portion  320   b  in front of the flange portion  324 . The first bellows portion  318   b  of the outer sheath  318  is accommodated in this outer sheath accommodation space  325 . A front side fixing ring  318   c  which is fixed at the end portion of the inner cylindrical portion  320   a  is formed at the end portion of this first bellows portion  318   b . Moreover, a front side fixing ring  319   c  which is fixed on the outer peripheral surface of the inner cylindrical portion  320   a  is formed at the end portion of the second bellows portion  319   a  of the inner sheath  319 . This front side fixing ring  319   c  is arranged on the rear side apart from the flange portion  324  of the inner cylindrical portion  320   a.    
      Additionally, in the mouthpiece member  317 , a fluid path  326  through which a working fluid such as pressurized air is supplied is formed between the outer sheath  318  and the inner sheath  319  of the external sheath  314 . An inner end portion of this fluid path  326  communicates with a part between the outer sheath  318  and the inner sheath  319  of the mouthpiece member  317 . Further, an outer end portion of the fluid path  326  is coupled with an air supply mouthpiece  327  arranged on an outer peripheral surface of the mouthpiece member  317 . One end portion of an air supply tube  328  is coupled with this air supply mouthpiece  327 . The other end portion of this air supply tube  328  is coupled with non-illustrated air supply means  329  such as an air supply pump. Furthermore, when the external sheath  314  of the insertion support tool  304  is extended, a working fluid such as pressurized air is supplied from this air supply tube  328  to a part between the outer sheath  318  and the inner sheath  319  through the air supply mouthpiece  327  and the fluid path  326 , and the external sheath  314  is extended in the inserting direction of the inserting portion  303 .  
       FIG. 50  shows an end side extension unit  313 . This end side extension unit  313  has a soft bag-shaped external sheath  341  which can be extended in the inserting direction of the inserting portion  303  of the large-intestine endoscope  302 , a substantially cylindrical rear side frame member  342  which is coupled with a base end portion of this external sheath  341 , and an end side frame member  343  which is coupled with an end portion of the external sheath  341 .  
      The inserting portion  303  of the large-intestine endoscope  302  can be inserted into a cylinder of the rear side frame member  342 . A large-diameter portion  342   a  is provided on a base end portion side of the rear side frame member  342 . An end cylindrical portion  342   b  whose diameter is smaller than that of any other part and allows insertion of the inserting portion  303  of the large-intestine endoscope  302  is provided on an end portion side of the rear side frame member  342 .  
      Moreover, the external sheath  341  has an outer sheath  344  and an inner sheath  345 . A rear side fixing ring  344   a  which is fixed at the large-diameter portion  342   a  of the rear side frame member  342  is formed at a base end portion of the outer sheath  344 . Additionally, an end side of the outer sheath  344  is extended toward the end side frame member  343 . Further, a folded first bellows portion  344   b  is formed on this extended portion side.  
      A folded second bellows portion  345   a  is formed in the inner sheath  345 . This second bellows portion  345   a  is arranged on the end cylindrical portion  342   b  of the rear side frame member  342 . Furthermore, a rear side fixing ring  345   b  which is fixed at the base end portion of the end cylindrical portion  342   b  is formed at a base end portion of this second bellows portion  345   a.    
      An annular flange portion  347  having a large diameter is provided to protrude from an outer peripheral surface of the end side frame member  343  on the base end portion side. Moreover, an outer sheath accommodation portion  348  is formed on the outer peripheral surface of the end side frame member  343  in front of the flange portion  347 . The first bellows portion  344   b  of the outer sheath  344  is accommodated in this outer sheath accommodating portion  348 . A front side fixing ring  344   c  which is fixed at the end portion of the end side frame member  343  is formed at the end portion of this first bellows portion  344   b . Further, in the inner sheath  345 , a front side fixing ring  345   c  which is fixed on the outer peripheral surface of the end side frame member  343  is formed at the end portion of the second bellows portion  345   a . This front side fixing ring  345   c  is arranged on the rear side of the end side frame member  343  apart from the flange portion  347 .  
      Furthermore, a suction path  349  for enabling a suction force between the outer sheath  344  and the inner sheath  345  of the external sheath  341  is formed in the rear side frame member  342 . An inner end portion of this suction path  349  communicates with a part between the outer sheath  344  and the inner sheath  345  of the rear side frame member  342 . Moreover, an outer end portion of the suction path  349  is coupled with a suction tube  350 . This suction tube  350  is coupled with suction means  351  such as a non-illustrated suction pump.  
      Additionally, when the end side extension unit  313  is not operated, a suction force from the suction tube  350  is exercised between the outer sheath  344  and the inner sheath  345  of the rear side frame member  342  through the suction path  349  so that the end side extension unit  313  is held in the contracted shape. Further, when the end side extension unit  313  is operated, the suction force which is exercised between the outer sheath  344  and the inner sheath  345  of the rear side frame member  342  is interrupted. In this case, the external sheath  341  is extended in the inserting direction of the inserting portion  303  in accordance with an inserting operation of the inserting portion  303  of the large-intestine endoscope  302 .  
      Furthermore, the end side frame member  343  has an endoscope attachment hole  331  at a substantial shaft center portion thereof. A front side of this endoscope attachment hole  331  is sealed by a transparent cover glass  332 . Moreover, the end hard portion  308  of the inserting portion  303  of the large-intestine endoscope  302  is coupled with the endoscope attachment hole  331  of the end side frame member  343  in a fitting state.  
      Additionally, a soft coupling tube  352  is installed between the main extension unit  312  and the end side extension unit  313 . This coupling tube  352  is arranged at a position corresponding to the curving portion  307  of the large-intestine endoscope  302 . Therefore, the coupling tube  322  can freely transform in accordance with a curving operation of the curving portion  307  of the large-intestine endoscope  302 .  
      A function of the above-mentioned configuration will now be described. At the time of an operation of inserting the inserting portion  303  of the large-intestine endoscope  302  into the large intestine (a rectum) H 2  from the anus H 1  of a patient H, the endoscope insertion apparatus  301  according to this embodiment is used in a state where the insertion support tool  304  is previously attached to the inserting portion  303  of the large-intestine endoscope  302  before insertion. In a state before inserting the inserting portion  303  of the large-intestine endoscope  302  into the insertion support tool  304 , the insertion support tool  304  is held with the external sheath  314  of the main extension unit  312  and the external sheath  341  of the end side extension unit  313  being respectively contracted. In this state, an operation of attaching the insertion support tool  304  with respect to the inserting portion  303  of the large-intestine endoscope  302  (an insertion support tool attachment step) is carried out.  
      At the time of this insertion support tool attachment operation, the inserting portion  303  of the large-intestine endoscope  302  is inserted into the cylinder of the mouthpiece member  317  from the end side through the opening portion  317   e  on the base end surface of the mouthpiece member  317  of the insertion support tool  304 . Further, as shown in  FIG. 50 , the end hard portion  308  of the inserting portion  303  is coupled with the endoscope attachment hole  331  of the end side frame member  343  in the fitting state so that an assembled unit  333  in which the insertion support tool  304  is assembled at the end portion of the inserting portion  303  of the large-intestine endoscope  302  is set.  
      After attachment of the insertion support tool  304 , the assembled unit  333  is inserted into the large intestine (the rectum) H 2  from the anus H 1  of the patient H (a first insertion step). At the time of this inserting operation, the insertion support tool  304  is inserted into the anus H 1  of the patient H from the end side frame member  343  side of the insertion support tool  304 . At this time, since the anus H 1  of the patient H is usually closed by a sphincter muscle, the operation of pushing the assembled unit  333  into the anus H 1  of the patient H while spreading the sphincter muscle of the anus H 1 .  
      Furthermore, after the insertion support tool  304  is fixed in the anus H 1 , a working fluid such as pressurized air is supplied to a part between the outer sheath  318  and the inner sheath  319  of the main extension unit  312  through the air supply mouthpiece  327  and the fluid path  326  from the air supply tube  328 . At this time, supply of the working fluid inflates a space between the outer sheath  318  and the inner sheath  319  of the external sheath  314 .  
      Therefore, the entire external sheath  314  is extended in the inserting direction of the inserting portion  303  of the large-intestine endoscope  302 . As a result, the insertion support tool  304  moves forward in a state where the end unit  316  is pushed forward with respect to the based unit  315 . At this time, the inserting portion  303  of the large-intestine endoscope  302  is moved forward together with the end unit  316  in the inserting direction of this inserting portion  303  (a second insertion step).  
      Thereafter, when the end portion of the insertion support tool  304  reaches a sharp intestinal canal bent portion in the large intestine H 2  of the patient as shown in  FIG. 51A , the part of the coupling tube  352  between the main extension unit  312  and the end side extension unit  313  (the part of the curving portion  307  of the large-intestine endoscope  302 ) is arranged at this position. When the working fluid is further supplied to the external sheath  314  of the main extension unit  312  in this state, the part of the curving portion  307  of the large-intestine endoscope  302  lodges in this sharp intestinal canal bent portion in the large intestine H 2  and cannot move forward as shown in  FIG. 51B .  
      Therefore, in such a case, the end side extension unit  313  is activated. When this end side extension unit  313  is activated, driving of the suction means  351  is stopped. In this case, the suction force which is exercised between the outer sheath  344  and the inner sheath  345  of the rear side frame member  342  is interrupted. In this state, the inserting portion  303  of the large-intestine endoscope  302  is pushed in the inserting direction. The external sheath  341  is extended in the inserting direction of the inserting portion  303  in accordance with the pushing operation of this inserting portion  303  as shown in  FIG. 51C  (a third insertion step). As a result, a part of the curving portion  307  of the large-intestine endoscope  302  is pulled into the end side extension unit  313  and moves over the sharp intestinal canal bent portion in the large intestine H 2  of the patient.  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in the endoscope insertion apparatus  301  according to this embodiment, attaching the inserting support tool  304  at the inserting portion  303  of the large-intestine endoscope  302  can extend the soft external sheath  314  of the main extension unit  312  of the insertion support tool  304  in the inserting direction of the inserting portion  303  at the time of inserting the inserting portion  303  of the large-intestine endoscope  302 , thereby supporting the inserting operation of the inserting portion  303  of the large-intestine endoscope  302 . Therefore, it is possible to readily perform the operation of inserting the inserting portion  303  of the large-intestine endoscope  302  into the large intestine (the rectum) H 2  of the patient H.  
      Moreover, in the endoscope insertion apparatus  301  according to this embodiment, the end side extension unit  313  is provided in front of the main extension unit  312 . Additionally, when the end portion of the insertion support tool  304  reaches the sharp intestinal canal bent portion in the large intestine H 2  of the patient during the operation of inserting the inserting portion  303  of the large-intestine endoscope  302  into the large intestine (the rectum) H 2  of the patient H, there may possibly occur a phenomenon that the part of the curving portion  307  of the large-intestine endoscope  302  lodges in this sharp intestinal canal bent portion in the large intestine H 2  and cannot move forward as shown in  FIG. 51B  even if the working fluid is further supplied to the external sheath  314  of the main extension unit  312 . In such a case, activating the end side extension unit  313  can extend the external sheath  341  in the inserting direction of the inserting portion  303  as shown in  FIG. 51C  in accordance with the pushing operation of the inserting portion  303 , thereby eliminating the phenomenon that the end portion of the insertion support tool  304  cannot move forward. As a result, it is possible to smoothly and assuredly perform the operation of inserting the assembled unit  333  into the large intestine H 2  of the patient H.  
      It is to be noted that the description has been given as to the example of using the suction means in this embodiment, the suction means may have pressurization means (not shown) for increasing a pressure between the outer sheath  344  and the inner sheath  345 . Further, a pressurization control switch (not shown) which is used by an operator to control a timing of pressurization is provided to the pressurization means, and the operator can operate the pressurization control switch at an arbitrary timing to turn on/off pressurization. When the suction means further has the pressurization means, the end side extension unit  313  can be forcibly extended, and the inserting portion  303  is pulled and further inserted into the large intestine by the end side extension unit  313  in accordance with the extending operation of the end side extension unit  313 .  
      According to the above-described configuration, when the operator tries to push the inserting portion  303  forward, it is possible to obtain an effect that the end side of the inserting portion  303  can be further inserted into the large intestine irrespective of the pushing force of the inserting portion  303  under a situation where the pushing force is not transmitted to the end side of the inserting portion  303  and the end side of the inserting portion  303  cannot be moved.  
      FIGS.  52  to  53 C show a 23rd embodiment according to the present invention. This embodiment is obtained by changing the configuration of the insertion support tool  304  of the endoscope insertion apparatus  301  of the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, although the 22nd embodiment shows the configuration in which a suction force from the suction tube  350  is utilized as the means for holding the end side extension unit  313  of the insertion support tool  304  in a non-activated state, an operation wire  361  which restricts an advancing operation of an end side frame member  343  is provided in an insertion support tool  304  according to this embodiment. As shown in  FIG. 52 , a fixed end portion  362  at an end of this operation wire  361  is fixed at a rear end portion of the end side frame member  343 .  
      The operation wire  361  is extended to a mouthpiece member  317  side of the insertion support tool  304  in a state where the operation wire  361  is inserted in a wire guide  363 . A fixed end portion  363   a  at an end of the wire guide  363  is fixed at a rear end portion of a rear side frame member  342 .  
      Moreover, a wire fixing portion  364  is provided to the mouthpiece member  317 . As shown in  FIG. 53A , this wire fixing portion  364  has a wire take-up roller  365  which takes up the operation wire  361 . A rotary disk  366  is fixed at one end portion of a rotary shaft  365   a  of this wire take-up roller  365 . As shown in  FIG. 53B , a plurality of locking holes  366   a  are aligned on this rotary disk  366  along a circumferential direction thereof.  
      Additionally, a roller fixing lever  367  is provided to the wire fixing portion  364 . One end portion of this roller fixing lever  367  is supported to be capable of swiveling around a swiveling shaft  368 . A locking claw  369  is provided at the other end portion of the roller fixing lever  367 . This locking claw  369  is selectively releasably locked in any locking hole  366   a  of the rotary disk  366 . Further, as shown in  FIG. 53A , when the locking claw  369  of the roller fixing lever  367  is locked in any locking hole  366   a  of the rotary disk  366 , rotation of the wire take-up roller  365  is stopped to restrict the advancing operation of the end side frame member  343 .  
      Furthermore, as shown in  FIG. 53C , when the roller fixing lever  367  is swiveled to a position at which the locking claw  369  of the roller fixing lever  367  comes off the locking hole  366   a  of the rotary disk  366 , rotation of the wire take-up roller  365  is enabled to move forward the end side frame member  343 .  
      A function of this embodiment having the above-mentioned configuration will now be described. In this embodiment, the end side extension unit  313  of the insertion support tool  304  is switched between a non-activated state and an activated state in accordance with the operation of the roller fixing lever  367  of the wire fixing portion  364 . Therefore, this embodiment can obtain the same function and effect as those of the insertion support tool  304  according to the 22nd embodiment.  
      Moreover, in this embodiment, since the locking claw  369  of the roller fixing lever  367  is locked in any locking hole  366   a  of the rotary disk  366  when the end side extension unit  313  of the insertion support tool  304  is held in the non-activated state, it is possible to assuredly avoid extension of the external sheath  341  of the end side extension unit  313  when the end side extension unit  313  is in the non-activated state. Therefore, the usability of the end side extension unit  313  of the insertion support tool  304  can be improved.  
       FIGS. 54A  to  55 B show a first modification of the wire fixing portion  364  assembled with respect to the insertion support tool  304  according to the 23rd embodiment (see FIGS.  52  to  53 C). In a wire fixing portion  364  according to this modification, a wire fixing claw  371  which fixes an operation wire  361  is provided to a mouthpiece member  317  as shown in  FIGS. 54A and 54B . An advancing operation of an end side frame member  343  is restricted when the operation wire  361  is fixed by this wire fixing claw  371 . Further, as shown in  FIGS. 55A and 55B , when the wire fixing claw  371  is cut off, the restriction of the operation wire  361  can be released to move forward the end side frame member  343 .  
      In this modification, the advancing operation of the end side frame member  343  is restricted when the operation wire  361  is fixed by the wire fixing claw  371 , but cutting off the wire fixing claw  371  can release the restriction of the operation wire  361  to move forward the end side frame member  343 . Therefore, this modification can obtain the same function as that of the insertion support tool  304  according to the 22nd embodiment, thereby demonstrating the same effect as that of the insertion support tool  304  according to the 22nd embodiment.  
       FIGS. 56A and 56B  show a second modification of the wire fixing portion  364  assembled with respect to the insertion support tool  304  according to the 23rd embodiment (see FIGS.  52  to  53 C). In a wire fixing portion  364  according to this modification, a wire fixing button  381  is provided as shown in  FIGS. 56A and 56B . A shaft portion  382  of this wire fixing button  381  is inserted into a through hole  384  formed in a mouthpiece member  317 . Moreover, a coil spring  383  which holds the wire fixing button  381  at a fixed position shown in  FIG. 56A  is provided to the wire fixing portion  364 .  
      Additionally, a wire insertion hole portion  382   a  into which an operation wire  361  is inserted is formed in the shaft portion  382  of the wire fixing button  381 . In a state where the wire fixing button  381  is held at the fixed portion shown in  FIG. 56A , this wire insertion hole portion  382   a  is inserted in the through hole  384  of the mouthpiece member  317 . Therefore, the operation wire  361  inserted in the wire insertion hole portion  382   a  of the shaft portion  382  of the wire fixing button  381  is restricted to a state where the operation wire  361  cannot move, due to the spring force of the coil spring  383 . In this state, an advancing operation of an end side frame member  343  is restricted. Further, as shown in  FIG. 56B , when the wire fixing button  381  is pushed in against a spring force of the coil spring  383 , the wire insertion hole portion  382   a  of the wire fixing button  381  is pushed out of the through hole  384  of the mouthpiece member  317 . As a result, the restriction of the operation wire  361  is released to enable the advancing operation of the end side frame member  343 .  
      In the wire fixing portion  364  according to this modification, the end side extension unit  313  of the insertion support tool  304  is switched between a non-activated state and an activated state by the operation of the wire fixing button  381 . Therefore, this embodiment can obtain the same function as that of the insertion support tool  304  according to the 22nd embodiment, and hence this modification can demonstrate the same effect as that of the insertion support tool  304  according to the 22nd embodiment.  
       FIGS. 57 and 58  show a 24th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the insertion support tool  304  of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, a balloon  391  is provided as means for holding an end side extension unit  313  of an insertion support tool  304  in a non-activated state. This balloon  391  is fixed on an inner peripheral surface of a rear side frame member  342 . Furthermore, an air supply tube line  392  is formed in the rear side frame member  342 . An inner end portion of this air supply tube line  392  communicates with the inside of the balloon  391 . An outer end portion of the air supply tube line  392  is coupled with one end of an air supply tube  393 . The other end of the air supply tube  393  is coupled with an air supply control portion which controls supply/discharge of a working fluid such as air.  
      Moreover, as shown in  FIG. 57 , in a state where the balloon  391  is inflated, an inner peripheral surface of the balloon  391  is brought into contact with a curving portion  307  part of a large-intestine endoscope  302  with pressure to restrict an advancing operation of an end side frame member  343 . Additionally, as shown in  FIG. 58 , in a state where the balloon  391  is contracted, the inner peripheral surface of the balloon  391  is moved away from the part of the curving portion  307  of the large-intestine endoscope  302 , thereby moving forward the end side frame member  343 . As a result, an external sheath  341  of an end side extension unit  313  can be extended in an inserting direction of an inserting portion  303  of the large-intestine endoscope  302 .  
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, the end side extension unit  313  of the insertion support tool  304  is switched between a non-activated state and an activated state by the operation of the balloon  391 . Therefore, this embodiment can obtain the same function as that of the insertion support tool  304  according to the 22nd embodiment, and hence this modification can demonstrate the same effect as that of the insertion support tool  304  according to the 22nd embodiment.  
      Further, FIGS.  59  to  62 B show a 25th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the insertion support tool  304  of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, there is provided an end side extension unit contraction mechanism  400  which uses the operation wire  361  according to the 23rd embodiment (see FIGS.  52  to  53 C) to pull an end side extension unit  313  in a contracting direction. In this end side extension unit contraction mechanism  400 , a pulley  401  is provided on an inner peripheral surface of an end side frame member  343 . An end portion of an operation wire  361  is wound around this pulley  401 . The end portion of the operation wire  361  folded back by this pulley  401  is fixed at a front end portion of a rear side frame member  342 .  
      Furthermore, a rotating operation handle  411  is fixed to a mouthpiece member  317  at one end portion of a rotary shaft  365   a  of a wire take-up roller  365 . Operating this rotating operation handle  411  can manipulate the operation wire  361  in either a direction along which the operation wire  361  is taken up by the wire take-up roller  365  or a direction along which the operation wire  361  is unreeled from the wire take-up roller  365 . Here, operating the rotating operation handle  411  in the direction along which the operation wire  361  is taken up by the wire take-up roller  365  can pull the end side extension unit  313  in the contracting direction.  
      Thus, the apparatus having the above-mentioned configuration can demonstrate the following effects. That is, in the endoscope insertion apparatus  301  according to this embodiment, an external sheath  341  of the end side extension unit  313  is extended in an inserting direction of an inserting portion  303  of the large-intestine endoscope  302  to insert the inserting portion  303  of the large-intestine endoscope  302 , and then the rotating operation handle  411  is operated in the direction along which the operation wire  361  is taken up by the wire take-up roller  365 , thereby contracting the external sheath  341  of the end side extension unit  313  to an original length thereof. Therefore, the end side extension unit  313  can be used many times, as required.  
       FIG. 63  shows a modification of the driving device of the end side extension unit  313  of the insertion support tool  304  according to the 25th embodiment (see FIGS.  59  to  62 B). In this modification, a driving motor  421  is provided in place of the manual rotating operation handle  411 . Thus, this modification can obtain the same function as that of the insertion support tool  304  according to the 25th embodiment, and hence this modification can demonstrate the same effect as that of the insertion support tool  304  according to the 25th embodiment.  
       FIGS. 64 and 65  show a 26th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, a plurality of indices  431   a  to  431   d  which indicate a length from an end of an insertion support tool  304  in a state where an inserting portion  303  of a large-intestine endoscope  302  is assembled in the insertion support tool  304  are provided to the inserting portion  303  of the large-intestine endoscope  302  which is assembled in the insertion support tool  304  and used in this state. Here, when a length L 1  from the end of the insertion support tool  304  is, e.g., 200 mm, the index  431   a  having the number “20” is indicated on the inserting portion  303  of the large-intestine endoscope  302 . Likewise, when a length L 2  from the end of the insertion support tool  304  is, e.g., 300 mm, the index  431   b  having the number “30” is indicated on the inserting portion  303  of the large-intestine endoscope  302 .  
      Further, in this embodiment, as shown in  FIG. 65 , a length of the inserting portion  303  of the large-intestine endoscope  302  pulled into the insertion support tool  304  can be confirmed by visually observing the number of each of the indices  431   a  to  431   d  indicated on the inserting portion  303  of the large-intestine endoscope  302  at a position of a mouthpiece member  317  of the insertion support tool  304 . As a result, an insertion length of the inserting portion  303  of the large-intestine endoscope  302  into a body cavity can be confirmed.  
      Thus, the apparatus having the above-mentioned configuration demonstrates the following effects. That is, in this embodiment, an insertion length into a body cavity can be confirmed by visually observing the number of each of the indices  431   a  to  431   d  indicated on the inserting portion  303  of the large-intestine endoscope  302  at the position of the mouthpiece member  317  of the insertion support tool  304 , and hence an end position of the inserting portion  303  of the large-intestine endoscope  302  can be readily grasped. Furthermore, an impossible insertion state can be easily detected.  
       FIGS. 66 and 67  show a 27th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, a plurality of indices  441   a  to  441   e  are provided on an inserting portion  303  of a large-intestine endoscope  302 , which is assembled in an insertion support tool  304  and used in this assembled state, at equal intervals from an end of the insertion support tool  304  in a state where the inserting portion  303  of the large-intestine endoscope  302  is assembled in the insertion support tool  304 . Here, when a length of a part of the mouthpiece member  317  of the insertion support tool  304  which is exposed to the outside of a body is X, a numeric value obtained by adding a length L 3 , L 4  . . . from the end of the insertion support tool  304  to each of the respective indices  441   a  to  441   e  to the length X of the part exposed to the outside of the body is indicated as a part of the respective indices  441   a  to  441   e.    
      Thus, the apparatus having the above-mentioned configuration demonstrates the following effects. That is, in this embodiment, an insertion length into a body cavity can be further accurately confirmed by visually observing the numeric value of each of the indices  441   a  to  441   d  indicated on the inserting portion  303  of the large-intestine endoscope  302  at the position of the mouthpiece member  317  of the insertion support tool  304 , and hence an end position of the inserting portion  303  of the large-intestine endoscope  302  can be readily accurately grasped.  
       FIGS. 68A and 68B  show a 28th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, as shown in  FIG. 68A , one end of a measurement wire  451  is fixed to an external sheath fixing member  320  of an end unit  316  of an insertion support tool  304 . Further, an insertion length measurement portion  452  is provided to a mouthpiece member  317 . A wire take-up roller  453  which takes up the measurement wire  451  is provided to this insertion length measurement portion  452 . An insertion length indicator  454  is provided to a rotary shaft of this wire take-up roller  453 .  
      Here, a relationship between the number of revolutions x of the wire take-up roller  453  and an insertion length y is expressed as follows: 
 
 y=ax+b  (a and b are constants) 
 
 Furthermore, the number of revolutions x of the wire take-up roller  453  is detected, and a value of y=ax+b is indicated in the insertion length indicator  454 . 
 
      Thus, the apparatus having the above-described configuration demonstrates the following effects. That is, in this embodiment, since a value of the insertion length y is indicated in the insertion length indicator  454 , the value of the insertion length y can be clearly specified.  
       FIGS. 69 and 70  show a 29th embodiment according to the present invention. This embodiment is obtained by changing the configuration of the endoscope insertion apparatus  301  according to the 22nd embodiment (see FIGS.  49  to  51 C) as follows.  
      That is, in this embodiment, as shown in  FIG. 69 , a label  461  which indicates a model name of a large-intestine endoscope  302  which is combined with an endoscope insertion support tool  304  is provided on the large-intestine endoscope  302 . Additionally, as shown in  FIG. 70 , a label  462  which indicates a model name of the large-intestine endoscope  302  to be combined is provided on the insertion support tool  304 .  
      Thus, the apparatus having the above-mentioned configuration demonstrates the following effects. That is, in this embodiment, even if the endoscope insertion support tool  304  is prepared with a specification which differs in accordance with each model of the endoscope  302  based on a thickness or the like of an inserting portion  303  of the endoscope  302 , a wrong combination can be avoided. Therefore, it is possible to prevent an extension defect or a device damage due to a wrong combination of the endoscope insertion support tool  304  and the endoscope  302 .  
      Further, the present invention is not restricted to the foregoing embodiments, and can be of course modified and carried out in many ways without departing from the scope of the invention.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general invention concept as defined by the appended claims and their equivalents.