Abstract:
The present invention is an endoscope apparatus including an endoscope comprising an observation optical system in which the angle of observable field of view for observing a therapeutic tool can be changed and an operating mechanism for changing the observable field of view; and an insertion guide tube for guiding the therapeutic tool into a body cavity, wherein the insertion guide tube is detachably positioned and supported in a predetermined position relative to the endoscope. With this apparatus, the therapeutic tool can be observed in an optimal observing state irrespective of whether the area to be observed is located near or far from a distal end of the endoscope.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-156151, filed on May 26, 2004, the entire contents of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an endoscope apparatus using a therapeutic tool therewith. For example, the therapeutic tool is an instrument introduced by an insertion guide tube with a bending function.  
         [0004]     2. Description of the Related Art  
         [0005]     In the related art, an endoscope treatment apparatus to be used with an insertion guide tube having a bending function for guiding an instrument is known (see JP-A-2000-33071). In this endoscope treatment apparatus, an operator adjusts the direction or the position of the distal end of the instrument guided into a body cavity by bending the insertion guide tube as needed.  
         [0006]     As described above, when the operator operates a therapeutic tool, which is the instrument guided by the insertion guide tube having a bending function in the body cavity, the treatment portion of the therapeutic tool must always be in the observable field of view of the endoscope.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     An endoscope apparatus according to a first aspect includes an endoscope including an observation optical system in which the angle of observable field of view for observing a therapeutic tool can be changed and an operating mechanism for changing the field angle of the observation optical system, and an insertion guide tube for guiding the therapeutic tool into a body cavity, wherein the insertion guide tube is detachably positioned and supported in a predetermined position relative to the endoscope.  
         [0008]     Accordingly, the tool to be operated by the insertion guide tube can be viewed at an optimum scale whether the area to be observed is close or far.  
         [0009]     According to a second aspect of the endoscope apparatus, in the endoscope apparatus according to the first aspect described above, the insertion guide tube has a bending function positioned and supported with an insertion portion of the endoscope.  
         [0010]     In this arrangement, since display on a screen of an easy-to-observe size is enabled without bending the insertion guide tube having a bending function strongly and sharply in a small range and in a small radius, the operator can move the therapeutic tools back and forth smoothly.  
         [0011]     According to a third aspect of the endoscope apparatus, in the endoscope apparatus according to the second aspect described above, the predetermined position can comprise an endoscope position located distally to a bending portion of the endoscope corresponding to an insertion guide tube position located proximally to a bendable area of the insertion guide tube.  
         [0012]     In this arrangement, stable and smooth movement of the bendable area is achieved.  
         [0013]     According to a fourth aspect of the endoscope apparatus, in the endoscope apparatus according to the first aspect described above, an image pickup device for picking up an image of the observable field of view into the endoscope apparatus is further provided, and an angle of field of view corresponding to a length of the longest diagonal line in an image pickup area of the image pickup device is set to a range between 60° and 100° for a narrow angle mode.  
         [0014]     This arrangement is practical and accordingly, the operator can easily use the endoscope apparatus.  
         [0015]     According to a fifth aspect of the endoscope apparatus, in the endoscope apparatus according to the first aspect described above, an image pickup device for picking up an image of the observable field of view into the endoscope apparatus is further provided, and an angle of field of view corresponding to a length of a longest diagonal line in an image pickup area of the image pickup device is set to a range between 100° and 150° for a wide angle mode, and between 60° and 100° for a narrow angle mode.  
         [0016]     In this arrangement, an optimal observation state can be obtained in the wide angle mode and the narrow angle mode, respectively.  
         [0017]     According to a sixth aspect of the endoscope apparatus, in the endoscope apparatus according to the first aspect described above, when changing the angle of field of view to observe in an enlarged scale, the observation optical system can be located in a same focal depth range before and after enlargement.  
         [0018]     In this arrangement, since the focal point is not displaced even in the case of observing in an enlarged scale, the object is prevented from becoming blurred.  
         [0019]     According to a seventh aspect of the endoscope apparatus, in the endoscope apparatus according to the sixth aspect described above, the focal depth of the observation optical system includes a position 40 mm distally from a position of a distal end of a lens at a distal-most position of the observation optical system.  
         [0020]     In this arrangement, since the position of the objective portion is located 40 mm distally from the position of the distal end of the lens, the actual use of the endoscope is convenient. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]     These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0022]      FIG. 1  is a partial perspective view showing a distal end of an endoscope treatment apparatus according to a first embodiment;  
         [0023]      FIG. 2  is a perspective view of the distal end of the endoscope treatment apparatus in a disassembled state according to the first embodiment;  
         [0024]      FIG. 3  is a cross sectional view of an objective unit integrated in the distal portion of an endoscope vertical to the axis thereof according to the first embodiment;  
         [0025]      FIG. 4A  is an explanatory drawing of the endoscope according to the first embodiment in which an angle of an objective observation optical system is large;  
         [0026]      FIG. 4B  is an explanatory drawing of the endoscope treatment apparatus according to the first embodiment, showing a display being made on a display unit thereof;  
         [0027]      FIG. 5A  is an explanatory drawing of the endoscope according to the first embodiment of the invention in which the angle of the objective observation optical system is small;  
         [0028]      FIG. 5B  is an explanatory drawing of the endoscope treatment apparatus according to the first embodiment, showing a display being made on the display unit;  
         [0029]      FIG. 6  is an explanatory drawing showing a relation between an angle W of the observable field of view of the objective observation optical system and a bending portion of an insertion guide tube in the endoscope according to the first embodiment;  
         [0030]      FIG. 7A  is an explanatory drawing showing a state of the bending portion of the insertion guide tube displayed on the screen of the display unit corresponding to one of the angle W of the observable field of view of the objective observation optical system in the endoscope according to the first embodiment;  
         [0031]      FIG. 7B  is an explanatory drawing showing a state of the bending portion of the insertion guide tube displayed on the screen of the display unit corresponding to one of the angle W of the observable field of view of the objective observation optical system in the endoscope according to the first embodiment;  
         [0032]      FIG. 7C  is an explanatory drawing showing a state of the bending portion of the insertion guide tube displayed on the screen of the display unit corresponding to one of the angle W of the observable field of view of the objective observation optical system in the endoscope according to the first embodiment;  
         [0033]      FIG. 8  is a partial perspective view showing a distal end of an endoscope treatment apparatus of another type;  
         [0034]      FIG. 9  is a partial perspective view showing a distal end of an endoscope treatment apparatus of still another type;  
         [0035]      FIG. 10  is a partial perspective view showing a distal portion of an endoscope treatment apparatus according to a second embodiment in a state of being used; and  
         [0036]      FIG. 11  is a partial perspective view showing a distal portion of the endoscope treatment apparatus according to a third embodiment in a state of being used. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     Preferred embodiments will be described below with reference to the accompanying drawings.  
         [0038]     Referring now to  FIG. 1  to  FIG. 9 , an endoscope apparatus according to a first embodiment will be described.  
         [0039]     As shown in  FIG. 1 , the endoscope apparatus according to this embodiment includes a flexible endoscope  1 , two insertion guide tubes  2   a ,  2   b , and two flexible guide tubes  3   a ,  3   b  through which the insertion guide tubes  2   a ,  2   b  are inserted independently. The flexible guide tubes  3   a ,  3   b  through which the insertion guide tubes  2   a ,  2   b  are inserted independently and an insertion portion  4  of the endoscope  1  are detachably connected by a connecting member  5  as an auxiliary member for positioning and supporting the same.  
         [0040]     The endoscope  1  includes the elongated insertion portion  4 , and a control section (not shown) provided at an operator&#39;s side of (proximally to) the insertion portion  4 . The insertion portion  4  of the endoscope  1  includes, as shown in  FIG. 1 , a distal portion  6  positioned at a distal end thereof, a bending portion  7  located on the operator&#39;s side of the distal portion  6 , and a flexible portion  8  located further on the operator&#39;s side of the bending portion  7 . The bending portion  7  of the endoscope  1  is, like the general endoscope, bent by an operation at the control section.  
         [0041]     The connecting member  5  includes, as shown in  FIG. 2 , two openings  9   a ,  9   b  fixedly connecting respective extremities of the guide tubes  3   a ,  3   b , and an opening  9   c  for fitting the distal portion  6  of the insertion portion  4  of the endoscope  1  for fixedly engaging the same. The respective openings  9   a ,  9   b ,  9   c  are parallel to each other, and the centers of the respective openings  9   a ,  9   b ,  9   c  are disposed so as to position at apexes of a triangle. A sidewall portion of the opening  9   c  to which the distal portion  6  of the endoscope  1  is fitted is formed with a slit  10  opening toward the side. The slit  10  is intended for facilitating widening of the opening  9   c  through a plastic deformation when fitting or removing the distal portion  6  of the endoscope  1  to/from the opening  9   c . Although the connecting member  5  is normally detachably attached to the distal portion  6  of the endoscope  1 , averting the bending portion  7  or the flexible portion  8 , it is also possible to engage the same to the end of the bending portion  7  on the operator&#39;s side end or to the flexible portion  8 .  
         [0042]     On the other hand, as shown in  FIG. 1 , insertion portions  15   a ,  15   b  of the respective insertion guide tubes  2   a ,  2   b  each include a distal portion  16  positioned at a distal end thereof, first bending portion  17  as bendable area positioned on the operator&#39;s side of the distal portion  16 , second bending portion  18  located on the operator&#39;s side of the first bending portion  17 , and flexible portion  19  provided continuously from the second bending portions  18  toward on the operator&#39;s side. The insertion portions  15   a ,  15   b  of the insertion guide tubes  2   a ,  2   b  are inserted separately through the respective guide tubes  3   a ,  3   b . At least the portions from the distal portions  16  to the first bending portion  17  and the second bending portion  18  can project from the distal opening ends of the guide tubes  3   a ,  3   b . The insertion guide tubes  2   a ,  2   b  are adapted to be used as manipulators for operating the therapeutic tool.  
         [0043]     The first bending portion  17  and the second bending portion  18  of the respective insertion guide tubes  2   a ,  2   b  are tubular portions that can be bent freely in the vertical and lateral directions as is known in the art. They can be adapted to be bendable by utilizing, for example, a plurality of bending pieces (not shown). The first bending portions  17  and the second bending portions  18  are respectively bent independently by pushing and pulling operation wires (not shown) respectively by remotely controlling the respective operating units of the insertion guide tubes  2   a ,  2   b  on the operator&#39;s side.  
         [0044]     The endoscope  1  in this embodiment is a straigiht-view type, and is provided with an observation window  21 , an illumination window  22 , and an instrument channel port  23  on the distal end surface of the distal portion  6 , as shown in  FIG. 1  and  FIG. 2  as in the case of a general endoscope.  
         [0045]     As shown in  FIG. 3 , the distal portion  6  is provided with an objective unit  27  including an objective observation optical system  25  for picking up (e.g., capturing) an image in the observable field of view from the observation window  21  and an image pickup device  26  for picking up the image in the observable field of view picked up by the objective observation optical system  25  integrated therein. The objective observation optical system  25  is of a scope system with magnification function, in which lenses are assembled to lens retaining frames  28   a ,  28   b ,  28   c  divided into a plurality of pieces.  
         [0046]     An objective lens group  30  including a transparent window member  29  constituting the observation window  21  and a field stop  31  are fixedly attached to the first lens retaining frame  28   a . The second lens retaining frame  28   b  is movable in the direction of the optical axis O A , and a movable lens or a movable lens group  33  is attached to the second lens retaining frame  28   b . The image pickup device  26  and an image forming lens group  34  for forming a field image in an image pickup area  26   a  of the image pickup device  26  are fixedly attached to the third lens retaining frame  28   c.    
         [0047]     As shown in  FIG. 3 , the movable second lens retaining frame  28   b  is slidably fitted to the inner surface of the third lens retaining frame  28   c , and is assembled so as to be movable in the direction of the optical axis O A  of the objective observation optical system  25 . The second lens retaining frame  28   b  is moved by an operating mechanism described later. The angle of field of view to be observed is changed by a movement of the movable lens  33  in the direction of the optical axis O A . The movable lens  33  includes a single concave lens disposed between the objective lens group  30  as a first lens group and the image forming lens group  34 . The movable lens  33  constitutes a field angle changing mechanism, so that the angle of observable field of view taken into the endoscope  1  is changed by sliding the movable lens  33  in the direction of the optical axis O A . The field angle changing mechanism is adapted to be capable of changing the field angle continuously or stepwise (incrementally).  
         [0048]     The operating mechanism for operating the field angle changing mechanism is an electric actuator  36  for moving the second lens retaining frame  28   b , as shown in  FIG. 3 . The electric actuator  36  includes an operating arm  37  that moves back and forth in the direction of the optical axis. The operating arm  37  extends into the lens retaining frame  28 C through a slit  38  formed on the wall of the fixed third lens retaining frame  28   c , and is connected to the movable lens retaining frame  28   b . The operator moves the movable lens  33  in the direction of the optical axis by operating selectively the operating arm  37  in the fore and aft optical direction by the electric actuator  36 , so that the angle of observable field of view by the objective observation optical system  25  can be changed to a desired value. As shown in  FIG. 3 , the electric actuator  36  is selectively driven by the operator operating a control section  39  such as a switch or the like provided on a grasping portion provided on the operator&#39;s side of the endoscope  1  corresponding thereto. The electric actuator  36  is connected to the control section  39  via a drive control line  39   a.    
         [0049]     An image of the observable field of view taken from the observation window  21  by the objective observation optical system  25  is formed in the image pickup area  26   a  of the image pickup device  26 , transmitted to a signal processing circuit (not shown) outside the endoscope through a transmission line  26   b , and converted into a screen image signal. The screen image is displayed on a screen  40  of the display unit shown in  FIG. 4B , and  FIG. 5B  respectively.  
         [0050]     Subsequently, the field angle selected by the field angle changing mechanism of the objective observation optical system  25  will be described. Normally, the angle referred to as the field angle when picking up the image of the observable field of view by the endoscope is an angle of range of the field of view which can be observed, corresponding to “W 1 ” in the normal state (distant view) shown in  FIG. 4A  or “W 2 ” in an enlarged scale shown in  FIG. 5A . In other words, the field angle in this embodiment represents a range of light entering from the observable field of view in front (distally) of the observation window  21  through the objective lens group  30  as the first lens group, passing as is through the movable lens  33  and the respective lenses in the image forming lens group  34 , and entering an effective image pickup area of the image pickup device  26  at the rearmost end to form an image on the light receiving surface, and is represented by the incident angle “W” with respect to the objective lens group  30 . Specific consideration will be made by applying this relation to the objective observation optical system  25  shown in  FIG. 3 . Light in the range wider than the “W 1 ” in the normal state (distant view) actually comes into the objective lens group  30 . The light is refracted according to the concave and convex surfaces of the respective lenses  30 ,  33 ,  34  in the optical system located along the optical axis O A , while part of the light being cut by the field stop  31  or the like provided as needed at the respective portions, is proceeded to the light receiving surface of the image pickup device  26 , and reaches the light receiving surface of the image pickup device  26 , where an image is picked up.  
         [0051]     However, since part of the light reaching the light receiving surface for picking up the image of the image pickup device  26 , which reaches the ends of the light receiving surface, varies, the light reaching the ends of the light receiving surface is cut and a remaining part of the light is used for image pickup as a signal for the screen image. The area to which the light to be used for image pickup, that is, to be converted as the image pickup signal, is an effective image pickup area corresponding to the field angle “W” at that time. Referring also to  FIG. 3 , an optical path of the objective observation optical system  25  will be described. The movable lens  33  shown by a solid line in  FIG. 3  is in a state of being moved to the front-most position, and the movable lens  33  shown by a broken line in  FIG. 3  is in a state of being moved to the rearmost position. As shown by the solid line in  FIG. 3 , in the state in which the movable lens  33  is slid to the front-most position, the field angle is such that light comes into the first objective lens group  30  from the range of the widest angle. The light path B of this incident light, which comes from the range of the narrowest field angle, is shown on the upper half of the objective unit  27 . In contrast, in a state in which the sliding portion of the movable lens  33  is slid to the rearmost position, light comes into the objective lens group  30  from the range of the widest field angle. The light path C of this incident light is shown on the lower half of the objective unit  27 . As will be seen from the broadening of the field angle shown in  FIG. 3 , when the movable lens  33  is moved forward, the field angle is reduced, and light comes in only from the small angle of field of view. In contrast, when the movable lens  33  is moved rearward, the field angle is increased, whereby light comes in from the large angle of field of view.  
         [0052]     Subsequently, in keeping with the fact described above, the relation between the width of the field angle “W” and enlargement of the image will be described referring to  FIG. 4A  and  FIG. 4B .  
         [0053]     When using the endoscope  1  in the state of a large field angle W 1  shown in  FIG. 4A , light in the range of large field angle “W 1 ” can come into the objective unit  27 . Therefore, the range which the observer can observe (the range displayed on the monitor screen  40  shown in  FIG. 4B ) corresponds to the entire range of the field angle “W 1 ”. In other words, a wide range of the subject is displayed on the monitor screen  40  as shown in  FIG. 4B . However, since the effective image pickup range of the image pickup device  26  does not change and the sizes of display areas L 1 , L 2  on the monitor screen  40  are constant, the subject to be observed is displayed in a small scale as a consequence.  
         [0054]     Also, when the endoscope  1  is used in a state of the smaller field angle “W 2 ” as shown in  FIG. 5A , since the effective image pickup range of the image pickup device  26  does not change and the sizes of display areas L 1 , L 2  on the monitor screen  40  are constant, the subject to be observed is consequently displayed in an enlarged scale as shown in  FIG. 5B .  
         [0055]     In other words, in order to observe in an enlarged scale, the field angle “W 2 ” is adjusted to be smaller than the normal state by moving the movable lens  33 . Then, since the area of the range of the narrow field angle “W 2 ” is displayed on the monitor screen  40  as an image from the reasons described above, if the sizes of the display areas L 1 , L 2  on the monitor screen  40  remain in the normal state, the object residing in the field of view is displayed in an enlarged scale, as shown in  FIG. 5B .  
         [0056]     As described above, the size of the object displayed on the monitor screen  40  can be changed by changing the field angle “W” under the conditions that the sizes of the display areas L 1 , L 2  on the monitor screen  40  do not change, and that the range of the area used as the image signal on the image pickup surface of the image pickup device  26  is not changed (“S 1 ” shown in  FIG. 4A  and “S 2 ” shown in  FIG. 5A  are the same (S 1 =S 2 )).  
         [0057]     Subsequently, the operation when using the endoscope treatment apparatus according to this embodiment will be described in detail.  
         [0058]     The operator resiliently fits the distal portion  6  of the insertion portion  4  of the endoscope  1  into the opening  9   c  of the connecting member  5  shown in  FIG. 2 , and fixedly engages the same. In this case, the operator opens (plastically deforms) the slit  10  of the connecting member  5  and fits the distal portion  6  into the opening  9   c . As shown in  FIG. 1 , the connecting member  5  is mounted to the distal portion  6  of the insertion portion  4  of the endoscope  1 , and the two guide tubes  3   a ,  3   b  extend along the insertion portion  4  of the endoscope  1 .  
         [0059]     Then, the operator inserts the insertion portion  4  of the endoscope  1  and the guide tubes  3   a ,  3   b  together into the body cavity. In this case, since the connecting member  5  is mounted to the distal portion  6  of the insertion portion  4  of the endoscope  1 , the connecting member  5  is in the state of being provided with the two guide tubes  3   a ,  3   b , and hence is capable of easily leading and introducing the two guide tubes  3   a ,  3   b . Since the distal ends of the flexible guide tubes  3   a ,  3   b  are located at the position of the distal portion  6  of the endoscope  1 , the distal portions of the insertion guide tubes  2   a ,  2   b  or of the therapeutic tool which are introduced into the body cavity through the guide tubes  3   a ,  3   b  are introduced inevitably in front (distally) of the distal portion  6  of the endoscope  1  as described later. Such a configuration results in an enhancement of the introduction operability of the insertion guide tubes  2   a ,  2   b  and the tools including the endoscope  1 .  
         [0060]     When inserting the insertion guide tubes  2   a ,  2   b  and endoscope  1  into the body cavity, it is also possible to use an over-tube (not shown) for inserting the endoscope  1  and the guide tubes  3   a ,  3   b  in a state of fixing the guide tubes  3   a ,  3   b  to the insertion portion  4  of the endoscope  1  as described above.  
         [0061]     Subsequently, after having introduced the insertion portion  4  of the endoscope  1  into the body cavity, as shown in  FIG. 1 , the operator inserts the insertion guide tubes  2   a ,  2   b  independently into the guide tubes  3   a ,  3   b , and cause the entire area including the distal portions  16 , the first bending portion  17 , and the second bending portion  18  to project into the body cavity from the distal end of the guide tubes  3   a ,  3   b.    
         [0062]     Then, the operator introduces one or more operational tools into the body cavity through the insertion guide tubes  2   a ,  2   b  while observing the interior of the body cavity by the endoscope  1 .  FIG. 1  shows a state in which an operative tool, for example, grasping forceps  51 ,  52  as instruments are introduced through the guide tubes  3   a ,  3   b  independently. The operator can also cause an additional operational tool such as an electrosurgical kinfe  54  to project from the instrument channel port  23  of the endoscope  1 .  
         [0063]     In this case, since the movable portions of the insertion guide tubes  2   a ,  2   b  projecting from the distal ends of the guide tubes  3   a ,  3   b  are retained at the connecting member  5  as a fulcrum, stable and smooth movement of the movable portions of the insertion guide tubes  2   a ,  2   b  is achieved. In the case in which the grasping forceps  51 ,  52  as the instrument are operated in the reverse direction by the insertion guide tubes  2   a ,  2   b , the power components exerted thereto in the opposite directions with the connecting member  5  as a common supporting point are cancelled with respect to each other. Therefore, the movable portions of the insertion guide tubes  2   a ,  2   b  move with the aforementioned fulcrum as a reference point, and hence a force exerted to the grasping forceps  51 ,  52  by the operator are reliably transmitted to an anatomy  53 .  
         [0064]     Subsequently, the state of observation in the body cavity by the endoscope  1  will be described. As shown in  FIG. 1 , the bending movable portion of the insertion guide tubes  2   a ,  2   b  and the distal portions of the grasping forceps  51 ,  52  projecting into the body cavity are located in the front (distal) area of the observation window  21  in the distal portion  6  of the endoscope  1 . The insertion guide tubes  2   a ,  2   b  and the distal portions of the grasping forceps  51 ,  52  are displayed in the display area on the screen  40  having a fixed size in various scales according to the value of the field angle W which is currently selected, as shown in  FIG. 7A ,  FIG. 7B , and  FIG. 7C .  
         [0065]     Therefore, the operator selects the angle of observable field of view by the objective observation optical system  25  according to the type of operation such as an operation, an observation, or a diagnosis as needed, and causes the subject on the monitor screen  40  to be displayed in a scale suitable to the type of operation.  
         [0066]     The image shown in  FIG. 7A  is a state in which the angle of observable field of view W is set to a normal size which is the same as the existing endoscope. In this embodiment, this field angle is “W 1 ” and corresponds, for example, to “130°” shown in  FIG. 6 . In this case, as shown in  FIG. 6 , the area including, and wider than, a constant width A which is at a distance of “20 mm” in front of (distal to) the distal end of the endoscope  1  is displayed in the display area of the fixed size on the monitor screen  40 .  
         [0067]     Therefore, a relatively wide range of the front area of the distal end of the endoscope  1  can be displayed on the monitor screen  40 . Such an observation like the existing endoscope is suitable for the case where the operator wants to determine the entire wide range of the front area of the endoscope  1 , for example, for the case of insertion of the endoscope or searching of the portion to be treated.  
         [0068]     However, when bending the insertion guide tubes  2   a ,  2   b  and operating the grasping forceps  51 ,  52 , the grasping forceps  51 ,  52  are shown in a small scale as shown in  FIG. 7A , and hence it is difficult for the operator to operate. In order to view the grasping forceps  51 ,  52  in a large scale, it is necessary to bend the bending movable portions of the insertion guide tubes  2   a ,  2   b  at a large angle in a small radius to bring the same closer to the distal end of the endoscope.  
         [0069]     However, since it is necessary to bend the bending portion of the insertion guide tube sharply by a stronger force by the operating wire, the parts at the bending portion or the operation wire is subjected to an excessive force. Also, at the sharply bent portion, the instruments cannot be moved back and forth smoothly. In addition, there are design and/or manufacture limits for the bending portion in terms of having a structure which is capable of being bent sharply.  
         [0070]     Therefore, the field angle W is selected so as to be capable of observing in the field angle which enables the operator to view the image in a larger scale, as shown in FIG.  7 B. In other words, the field angle is changed into the field angle “W 2 ” which is smaller than the field angle of the existing endoscope. For example, the field angle is assumed to be “90°” shown in  FIG. 6 . At this time, the entire area of the constant width A at a distance of “40 mm” in front of (distal to) the distal end of the endoscope  1 , as shown in  FIG. 6 , is displayed in the display area of the monitor screen  40  of a fixed size. Therefore, the area apart from the distal end of the endoscope  1  toward the front can be displayed on the monitor screen  40  in an enlarged scale. In the case of the field angle “W 2 ”, the area at the position relatively apart from the distal end of the endoscope  1  toward the front can be observed in an enlarged scale. Therefore, since the area apart from the distal end of the endoscope  1  toward the front can be observed in an enlarged scale, the operator can easily operate the grasping forceps  51 ,  52  by the insertion guide tubes  2   a ,  2   b , so that the images of the grasping forceps  51 ,  52  are enlarged and can be observed in an viewer-friendly state. The enlarged observation at the field angle of “W 2 ” is particularly suitable for the operation performed by using the therapeutic tools. In other words, the area in front of (distal to) the distal end of the endoscope can be viewed in an enlarged scale without sharply bending the bending portions of the insertion guide tubes  2   a ,  2   b  and therefore, avoiding the associated disadvantages of such a sharp bending.  
         [0071]     The state of the image shown in  FIG. 7C  corresponds to a state in which the angle of observable field of view W is set to the narrowest value and simultaneously the distal end of the endoscope is brought to a position, which corresponds to a close-up state. The field angle may be “W 2 ” described above. In other words, the close-up state in which the subject is enlarged to a magnification higher than the existing endoscope can be obtained easily by moving the distal end of the endoscope and selecting the field angle.  
         [0072]     As is clear from the fact described above, the size of the image which can be displayed on the monitor screen  40  can be adjusted as needed by the change of the field angle W, in which the angle “W” of the observable field of view by the objective observation optical system  25  is selected.  
         [0073]     In particular, when the field angle “W 2 ” is set to obtain the state of the image shown in  FIG. 7B , the bending movable portions of the insertion guide tubes  2   a ,  2   b  including the first bending portions  17  and the second bending portions  18  can be placed at positions projected apart from the front of the distal portion  6  of the endoscope  1  (distal to the distal end) as shown in solid lines in  FIG. 6 , whereby an allowance is provided in bending operation of the first bending portions  17  and the second bending portions  18 . In addition, the images of the grasping forceps  51 ,  52  are enlarged, and hence they can be operated while observing in a viewer-friendly state.  
         [0074]     Therefore, in this embodiment, the image can be displayed in the screen of an easy-to-observe size, and the tools such as the instrument can be operated easily even without bending the movable portion of the insertion guide tubes  2   a ,  2   b  including the first bending portions  17  and the second bending portions  18  strongly and sharply in a small range and a small radius. The parts of the bending portions  17 ,  18  of the insertion guide tubes  2   a ,  2   b  or the operation wire are prevented from being exerted with an excessive force. Furthermore, since the bending portions  17 ,  18  are not bent sharply, the instruments can be moved back and forth smoothly in the bending portions  17 ,  18  of the insertion guide tubes  2   a ,  2   b , whereby the operability is further enhanced. In addition, since it is not necessary to provide a structure in which the bending portions  17 ,  18  can be bent sharply, limit in design or manufacture of the bending portions  17 ,  18  is advantageously alleviated.  
         [0075]     In this embodiment, the entire movement of the manipulator that controls the therapeutic tools during the operation can be secured, and the wide range of observation for viewing the portion near the diseased portion entirely and the observation of the part to be operated in detail in an enlarged scale can be easily selected. In particular, the enlarged observation for determining the movement of the distal end of the manipulator or the therapeutic tool in detail can be easily selected, and hence operation such as moving the endoscope itself toward or away from the subject can be eliminated.  
         [0076]     The endoscope apparatus shown in  FIG. 8  is of a type in which the fixed position of the connecting member  5  with respect to the insertion portion  4  can be changed. The connecting member  5  can be mounted to a position near the distal end of the distal portion  6  as shown by solid lines in  FIG. 8 . However, when operating the therapeutic tool by the insertion guide tubes  2   a ,  2   b , the connecting member  5  can be moved backward (proximally) as shown by broken lines in  FIG. 8  and mounted to the insertion portion  4  of the endoscope  1 . The length of the movable bending areas of the bending portions  17 ,  18  of the insertion guide tubes  2   a ,  2   b  can be increased by the amount corresponding to the amount of retraction of the connecting member  5 . Therefore, an allowance is provided in bending of the bending portions  17 ,  18 .  
         [0077]     The endoscope shown in  FIG. 9  is configured in such a manner that an objective observation optical system unit  55  which is to be assembled into the distal portion  6  of the endoscope  1  can be projected from and retracted into the distal end of the distal portion  6  in the fore-and-aft direction. When the insertion guide tubes  2   a ,  2   b  are used, and the insertion guide tubes  2   a ,  2   b  are bent, the objective observation optical system unit  55  is projected forward from the distal end of the distal portion  6 , whereby the length of the bending movable areas of the bending portions  17 ,  18  of the insertion guide tubes  2   a ,  2   b  can be increased correspondingly. Therefore, the bent portions  17 ,  18  can be bent with allowance.  
         [0078]     In the endoscope of the type shown in  FIG. 8  or  FIG. 9  described above as well, when the mechanism for changing the field angle of the objective observation optical system  25  as described above is built in, the advantage of the mechanism that change the field angle can be obtained.  
         [0079]     In this embodiment, since the focal distance does not change before and after enlargement, there is an advantage in that the image can be viewed in an enlarged scale without moving the endoscope itself, for example, back and forth.  
         [0080]     According to this embodiment, since the scale of enlargement can be converted in a state in which the position of the endoscope  1  is fixed, and hence the objective portion can be viewed in an enlarged scale without changing the position of the endoscope  1 , or the entire portion can be overviewed, operability is enhanced.  
         [0081]     According to this embodiment described above, the objective observation optical system  25  employs a structure of a scope with magnification function in which the single concave lens at the midpoint of the lens group is moved. However, in actual use, the focus position of the objective observation optical system  25  does not have to be the best position, and as long as it is in approximate focus, there is no problem in the actual use and hence is acceptable. It is also possible to employ a type having a zooming mechanism in which the focal distance (the position in focus) is changed according to the change of the angle of observable field of view. Furthermore, it is also possible to design the same so that the image can be enlarged by reducing the field angle and the object at the closer position can be focalized, so that enlargement can be achieved by reducing the field angle.  
         [0082]     Although an example in which the electric actuator  36  is employed as the operating mechanism for changing the field angle is shown in this embodiment, other means are possible. For example, it is also possible to employ a mechanical operating system in which an operating element such as an operating knob provided at the control section on the operator&#39;s side is operated and the operating force is transmitted to the movable lens retaining frame  28   b  by the operating force transmitting mechanism such as a wire.  
         [0083]     Furthermore, although the insertion guide tubes  2   a ,  2   b  are guided by the use of the guide tubes  3   a ,  3   b  in this embodiment, it is also possible to mount the insertion guide tubes  2   a ,  2   b  directly to the connecting member  5  without using the guide tubes  3   a ,  3   b.    
         [0084]     Although the range of the angle of observable field of view taken into the observation optical system of the endoscope  1  may be set to a wide range as described above, when the angle of field of view corresponding to the length of the longest diagonal line in the image pickup area of the image pickup device  26  is set, for example, to the range from 60° to 100° in an enlarged state, practicability and usability are achieved.  
         [0085]     Also, when the field angle is set to the range from 100° to 150° for the normal observation (at a wide angle), and to the range from 60° to 100° in an enlarged state, the optimal state of observation can easily be respectively obtained.  
         [0086]     In addition, when observing in an enlarged state by the observation optical system, it is preferable that the focal depth before and after the enlargement is in the same focal depth range.  
         [0087]     Normally, since the objective portion is located at a distance of about 40 mm, it is preferable that the focal depth is located at a position in the vicinity of the position 40 mm apart from the position of the distal end of the distal-most lens of the observation optical system in terms of actual use of the endoscope.  
         [0088]     The focal depth can be represented generally by the distance from the distal end surface of the lens located at the distal-most position of the observation optical system. The focal depth is not the distance of one point, but the range in which the image seems to be substantially in focus, and hence the focal depth includes a certain range which is represented by the position referred to as the focal depth, which moves apart toward the front from the position of the distal end of the distal-most lens in the observation optical system.  
         [0089]     Subsequently, referring now to  FIG. 10 , an endoscope apparatus according to a second embodiment will be described. This embodiment employs an over-tube  60  as an auxiliary tool for detachably positioning and supporting the guide tubes  2   a ,  2   b  and the insertion portion  4  of the endoscope  1 . The guide tubes  2   a ,  2   b  and the insertion portion  4  of the endoscope  1  are guided by the over-tube  60 , and the endoscope  1  and the insertion guide tubes  2   a ,  2   b  are positioned and retained in a state of being correlated with each other.  
         [0090]     In this embodiment, since the over-tube  60  is employed, it is easy to replace the endoscope  1  and the insertion guide tubes  2   a ,  2   b . Other parts are the same as the first embodiment described above. Therefore, the same effects as described above are obtained in this embodiment as well.  
         [0091]     Referring now to  FIG. 11 , an endoscope treatment apparatus according to a third embodiment will be described. In this embodiment, part of the bending portion  18  near the operator&#39;s side is connected to the distal portion  6  of the endoscope  1  using a connecting member  71  while avoiding interference with the bending portions  17 ,  18  of the insertion guide tubes  2   a ,  2   b . Insertion portions  72  of the insertion guide tubes  2   a ,  2   b  are integrated into one piece. The bending portions  17 ,  18  of the two insertion guide tubes  2   a ,  2   b  are respectively extended from the distal end of the integrated insertion portion  72 . Then, the endoscope  1  and the insertion guide tubes  2   a ,  2   b  are positioned and detachably bundled by the connecting member  71  in a state in which the insertion portions  72  of the insertion guide tubes  2   a ,  2   b  are laid along the insertion portion  4  of the endoscope  1 .  
         [0092]     According to this embodiment, the effects as described above can be obtained, and in addition, a positional relationship between the bending portions  17 ,  18  of the two insertion guide tubes  2   a ,  2   b  can be determined. Therefore, the operation of the bending portions  17 ,  18  can advantageously be performed easily. Other parts are the same as the first embodiment described above. Therefore, with this embodiment as well, the above-described effects can be obtained.  
         [0093]     While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.