Patent Publication Number: US-2012046661-A1

Title: High-frequency treatment instrument

Description:
TECHNICAL FIELD 
     The present invention relates to a high-frequency treatment instrument. 
     BACKGROUND ART 
     High-frequency treatment instruments for medical use are employed for treatment of a diseased part in a body by applying a high-frequency current, and generally used with an endoscope. The high-frequency treatment instrument includes an elongate operating wire with a treatment element attached to its distal end portion, and a manipulating unit for axially moving the operating wire or rotating the same about its axis, on a proximal end. In use of such a high-frequency treatment instrument, a high-frequency cable connected to a high-frequency power source is connected to a high-frequency terminal of the manipulating unit, and a high-frequency current is applied to the diseased part through the operating wire for treatment of the diseased part such as resection. 
     This type of instruments can be found, for example, in patent documents 1 and 2. 
     In a snare instrument according to the patent document 1, a plug for applying a high-frequency current is provided on an axial manipulator (spool member) that can axially slide with respect to a manipulating unit (handle assembly). The handle assembly of this snare instrument includes a main body and a knob coaxially coupled to each other, so that rotating the knob about the axis causes the operating wire (shaft) and the treatment element (snare loop) to rotate (see  FIG. 11  of the patent document 1). 
     In a high-frequency treatment instrument according to the patent document 2, a plug for applying a high-frequency current is provided in a main body (base portion), and an manipulating unit for rotating and axially moving the treatment element is attached to a proximal side of the main body. The manipulating unit includes a ring-shaped manipulating element attached to the base portion with a fixed interval therebetween, and a slider movable back and forth with respect to the manipulating unit. Upon rotating the slider and the manipulating element with respect to the base portion, the operating wire and the treatment element are caused to rotate. 
     RELATED DOCUMENTS 
     Patent Documents 
     [Patent Document 1] JP-A No. 2003-506135 
     [Patent Document 2] JP-A No. 2007-325721 
     DISCLOSURE OF THE INVENTION 
     The high-frequency treatment instruments according to the patent documents 1 and 2, however, still have a room for improvement in terms of operability in moving back and forth or rotating the operating wire. 
     Regarding the snare instrument according to the patent document 1, since the high-frequency cable is connected to the axial manipulator, the self weight of the high-frequency cable is imposed on the axial manipulator when the axial manipulator is moved back and forth. Accordingly, the axial manipulator becomes heavier, in other words a greater axial force is required for moving the axial manipulator, which makes it difficult to subtly control the snare loop. 
     Regarding the high-frequency treatment instrument according to the patent document 2, since the high-frequency current plug is provided in a main body (base portion), the slider can be manipulated free from the self weight of the high-frequency cable, and hence better operability is obtained in terms of back and forth movement of the operating wire. However, since the ring-shaped manipulating element for rotating the operating wire about its axis is mounted on the proximal side of the main body (base portion) in the form of an assembly coupled with the slider, it is difficult to subtly control the rotation angle of the operating wire. 
     The present invention has been accomplished in view of the foregoing situation, and provides a high-frequency treatment instrument that allows an operating wire to be subtly controlled in a back and forth and rotational movement. 
     In an aspect, the present invention provides a high-frequency treatment instrument including a flexible tube to be inserted in a body cavity, an electrically conductive operating wire inserted through the flexible tube so as to move back and forth, a treatment element provided at a distal end portion of the operating wire and configured to treat a diseased part by application of a high-frequency current, and a manipulating unit attached to a proximal end portion of the flexible tube and configured to move the operating wire back and forth to thereby manipulate the treatment element, and to rotate the operating wire torsionally about a longitudinal axis thereof to thereby rotate the treatment element, wherein the manipulating unit includes a main body being attached a high-frequency cable that supplies a high-frequency current to the treatment element, a rotational manipulator rotatably attached to a distal side of the main body so as to rotate the operating wire about the longitudinal axis thereof, and an axial manipulator attached to a proximal side of the main body so as to axially move to thereby cause the operating wire to move back and forth. 
     In a specific embodiment of the present invention, the main body may include a conductive pipe made of a metal buried therein, the conductive pipe being electrically connected to the high-frequency cable and through which the operating wire is inserted, and the operating wire may include a cylindrical conductor that slides on the conductive pipe maintaining electrical connection to the conductive pipe. 
     In another specific embodiment of the present invention, the high-frequency treatment instrument may include a lead pipe made of a metal attached to an outer periphery of the proximal end portion of the operating wire, and the conductor may be provided on an outer surface of the lead pipe. 
     In still another specific embodiment of the present invention, the high-frequency treatment instrument may further include a mitigator that applies a biasing force to the operating wire in a direction opposite to an axial movement thereof. 
     In still another specific embodiment of the present invention, the treatment element may include a plurality of scissor pieces caused to open and close with respect to each other by a movement of the axial manipulator to move the operating wire back and forth, and the mitigator may apply the biasing force to the operating wire when the scissor pieces are made to open by a forward or backward movement of the operating wire. 
     In still another specific embodiment of the present invention, the operating wire may be caused to move backward or forward by the biasing force of the mitigator, from a maximum open state realized by the axial movement of the operating wire where an aperture of the scissor pieces is largest, and the scissor pieces may present an intermediate open state where the aperture is smaller than that of the maximum open state. 
     In still another specific embodiment of the present invention, the mitigator may be resiliently interposed between the main body and the axial manipulator. 
     In still another specific embodiment of the present invention, the mitigator may include a holder engaged with the operating wire with a predetermined engaging force to thereby restrict a back-and-forth movement of the axial manipulator, and a biasing member resiliently interposed between the holder and the axial manipulator, and the holder may become disengaged from the operating wire when a load greater than the predetermined engaging force is applied to the axial manipulator in the axial direction, to thereby allow the back-and-forth movement of the axial manipulator. 
     In still another specific embodiment of the present invention, the rotational manipulator may include a plurality of stepped portions formed on a proximal end portion thereof, the main body may include a multiple-stage fitting base formed on a distal end portion thereof, the fitting base being attached the rotational manipulator, and the plurality of stepped portions may make plane-to-plane contacts with the fitting base. 
     In still another specific embodiment of the present invention, the rotational manipulator may include a projection formed on the proximal end portion thereof, the projection being inserted through the fitting base, and the projection may include a stopper formed therearound so as to prevent the projection from coming off from the fitting base. 
     In still another specific embodiment of the present invention, the stopper may bias the rotational manipulator toward the proximal side of the main body. 
     In still another specific embodiment of the present invention, the axial manipulator may have an axially symmetrical shape. 
     In still another specific embodiment of the present invention, the high-frequency treatment instrument may further include an annular auxiliary ring pivotally attached to the main body and having an opening oriented in a direction intersecting with the axial direction, and the axial manipulator may be movable in the axial direction being restricted from rotating about the axis with respect to the main body. 
     In still another specific embodiment of the present invention, the rotational manipulator may be circumferentially exposed on an outer surface of the main body. 
     Here, the constituents of the present invention such as the manipulating unit and the high-frequency inlet do not always have to be individually independent, but may be arranged such that a plurality of constituents constitutes a unified member, that a plurality of members constitutes a constituent, that a constituent is a part of another constituent, or that a part of a constituent also serves as a part of another constituent. 
     In the high-frequency treatment instrument according to the present invention, the high-frequency cable is attached to the main body, and the rotational manipulator for rotating the operating wire about its axis and the axial manipulator for moving the operating wire back and force are provided independently from the main body. Accordingly, the operating wire can be moved back and forth or rotated free from the self weight of the high-frequency cable, which allows more subtle control of the operating wire compared with the snare instrument according to the patent document 1. 
     In addition, since the high-frequency treatment instrument according to the present invention is configured to apply a rotational torque to the operating wire on the distal side of the main body, the distance between the treatment element attached to the distal end of the operating wire and the position where the rotational torque is applied is shorter than in the high-frequency treatment instrument according to the patent document  2 , in which a rotational torque is applied to the operating wire on the proximal side of the main body. Such a configuration allows the treatment element to more quickly respond to the rotational manipulation of the operating wire. Thus, the present invention allows the operating wire to be subtly controlled in a back and forth and rotational movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages will become more apparent through preferred embodiments described hereunder and the accompanying drawings specified below. 
         FIG. 1  is a perspective view showing a high-frequency treatment instrument according to a first embodiment of the present invention; 
         FIG. 2  is a front view of the high-frequency treatment instrument according to the first embodiment; 
         FIG. 3A  is a front view showing a treatment element in an open state, and  FIG. 3B  is front view showing a treatment element in a closed state; 
         FIG. 4A  is a vertical cross-sectional view of a manipulating unit, and  FIG. 4B  is a transverse cross-sectional view thereof; 
         FIG. 5  is an enlarged view of a portion of  FIG. 4A ; 
         FIG. 6  is a cross-sectional view of a fitting base formed on a main body; 
         FIGS. 7A to 7C  are cross-sectional views of a manipulating unit of a high-frequency treatment instrument according to a second embodiment of the present invention,  FIG. 7A  showing a state where a slider is at a retreated position,  FIG. 7B  showing a state where the slider is at the forwardmost position, and  FIG. 7C  showing a state where an operating wire is slacked; 
         FIG. 8A  is a side view of a distal side of a holder constituting a mitigator, and  FIG. 8B  is a front view thereof; 
         FIG. 9A  is a vertical cross-sectional views showing a state before fitting the mitigator, and  FIG. 9B  is a vertical cross-sectional views showing a state after fitting the mitigator; and 
         FIGS. 10A to 10C  are cross-sectional partial views of a manipulating unit of a high-frequency treatment instrument according to a variation of the second embodiment,  FIG. 10A  showing a state where the slider is restricted from moving forward,  FIG. 10B  showing a state where the slider is moving forward, and  FIG. 10C  showing a state where the operating wire is slacked. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, embodiments of the present invention will be described referring to the drawings. In all the drawings, the same constituents will be given the same numeral, and the description thereof will not be repeated. 
     First Embodiment 
       FIG. 1  is a perspective view showing a high-frequency treatment  10  instrument according to a first embodiment of the present invention the present invention. In  FIG. 1 , a portion of an elongate flexible tube  50  is cut away. 
       FIG. 2  is a front view of the high-frequency treatment instrument  10  according to this embodiment. In the subsequent description, a lateral direction with respect to a longitudinal direction of the high-frequency treatment instrument  10  will be referred to as a front direction. 
     To start with, an outline of the high-frequency treatment instrument  10  according to this embodiment will be described. 
     The high-frequency treatment instrument  10  according to this embodiment includes a flexible tube  50  to be inserted in a body cavity, an electrically conductive operating wire  30  inserted through the flexible tube  50  so as to move back and forth, a treatment element  60  provided at a distal end portion of the operating wire  30  and configured to treat a diseased part by application of a high-frequency current, and a manipulating unit  20  attached to a proximal end portion of the flexible tube  50 . 
     The manipulating unit  20  is a mechanism for moving the operating wire  30  back and forth thereby moving the treatment element  60  and for rotating the operating wire  30  torsionally about its axis thereby rotating the treatment element  60 , and includes a main body  22 , a rotational manipulator  24 , and an axial manipulator  26 . 
     A high-frequency cable  70  through which a high-frequency current is supplied to the treatment element  60  is connected to the main body  22 . The rotational manipulator  24  is rotatably attached to a distal side of the main body  22  so as to rotate the operating wire  30  about the axis thereof. The axial manipulator  26  is attached to a proximal side of the main body  22  so as to axially move, to thereby cause the operating wire  30  to move back and forth. 
     Further details of the high-frequency treatment instrument  10  according to this embodiment will now be described. 
     The treatment element  60  employed in the high-frequency treatment instrument  10  moves interlocked with the back and forth movement of the operating wire  30 , and rotates interlocked with the rotation of the operating wire  30  about its axis. The treatment element  60  serves to treat a diseased part by application of a high-frequency current. 
     Although the configuration of the treatment element  60  is not specifically limited, this embodiment adopts a scissors type treatment element for incising a diseased part utilizing a linkage mechanism. Alternatively, a conventionally known device such as a knife type with a bent point or a wire snare loop may be employed as the treatment element  60 . The scissors type treatment element  60  includes, as will be subsequently described, a linkage mechanism driven by a back and forth movement of the operating wire  30 , and incises a diseased part while applying a high-frequency wave. In the case of the knife type treatment element, the bent point is hooked on a diseased part, and the treatment element is pulled toward the proximal side while applying a high-frequency wave, to incise the diseased part. In the case of the snare treatment element, the diameter of the snare is increased and decreased by a back and forth movement of the operating wire  30 , so as to bind a diseased part. 
     The operating wire  30  according to this embodiment is a wire rod made of a metal. The operating wire  30  is inserted through the flexible tube  50  constituted of a flexible material. 
     The material of the flexible tube  50  is not specifically limited, and either a conductive or non-conductive material maybe employed. In the case of employing a conductive material, it is preferable to provide a thin-film coating of an insulative material on the conductive inner surface of the flexible tube  50 . 
     Examples of the non-conductive material suitable for the flexible tube  50  include resin materials such as a fluorine resin, a polyimide resin, a polyethylene resin, a polypropylene resin, a polyurethane resin, a polyamide resin, and a polycarbonate resin. In particular, a fluorine resin is preferable because of excellent slidability with respect to a forceps channel through which the flexible tube  50  is inserted. 
     The treatment element  60  sticks out from the distal end opening of the flexible tube  50 . The treatment element  60 , the operating wire  30  and the flexible tube  50  are inserted through a lumen of an endoscope (not shown). 
     The manipulating unit  20  is a mechanism for pulling and pushing the operating wire  30 , or torsionally rotating the same about a longitudinal axis thereof. The manipulating unit  20  according to this embodiment essentially includes a main body  22 , a rotational manipulator  24 , and an axial manipulator  26 . 
     The main body  22  has a hollow cylindrical shape, and accommodates therein the proximal end portion of the operating wire  30 . The axial direction of the main body  22  and the extending direction of the operating wire  30  coincide with each other. 
     Accordingly, the term “axis” or “axial” herein refers to the extending direction of the operating wire  30 , unless otherwise defined specifically. 
     The rotational manipulator  24  is attached to the distal side of the main body  22 . The rotational manipulator  24  is engaged with the operating wire  30 , such that upon rotating the rotational manipulator  24  about the axis the treatment element  60  is caused to rotate about the axis, as indicated by curved arrows in  FIGS. 1 and 2 . 
     The rotational manipulator  24  is located on the distal end portion of the manipulating unit  20 , more particularly on the distal side of the main body  22 . The term “distal end portion” of the manipulating unit  20  herein refers to a longitudinal region having a predetermined extension. 
     In the high-frequency treatment instrument  10  according to this embodiment, the rotational manipulator  24  is located at the tip end of the manipulating unit  20 . 
     The rotational manipulator  24  is attached over the distal side face of the main body  22  in a cap shape. The rotational manipulator  24  is circumferentially exposed on the outer periphery of the main body  22 . 
     The rotational manipulator  24  includes a corrugated knurling formed along the outer circumferential surface thereof, the outer circumferential surface about the axis of the manipulating unit  20 . 
     The high-frequency treatment instrument  10  according to this embodiment can be accessed by an operator from any direction about the axis with respect to the rotational manipulator  24 . Since the rotational manipulator  24  is circumferentially exposed on the outer periphery of the main body  22 , the rotational stroke of the rotational manipulator  24  is unlimited. In the case where only a part of the outer periphery of the knob is exposed, as the handle assembly of the snare instrument according to the patent document 1, it is difficult to continuously rotate the treatment element  60  over a predetermined rotational angle (for example, 180 degrees). More specifically, to rotate the treatment element by an angle exceeding 180 degrees when operating the snare instrument according to the patent document 1, the operator has to once remove his/her finger from the knob upon having rotated the knob to the end of the rotational stroke, and then move the finger to the start point of the rotational stroke in order to resume the rotating operation. Thus it is impossible to continuously manipulate the knob, which restricts the operator from delicately rotating the treatment element. 
     In contrast, with the high-frequency treatment instrument  10  according to this embodiment, since the rotational stroke of the rotational manipulator  24  is unlimited, the treatment element  60  can be made to continuously rotate irrespective of the desired rotational angle of the treatment element  60 . 
     As indicated by straight arrows in  FIGS. 1 and 2 , upon axially sliding the axial manipulator  26  with respect to a shaft  228  of the main body  22  the treatment element  60  is caused to open and close. 
       FIGS. 3A and 3B  are enlarged views of a portion III circled by broken lines in  FIG. 2 .  FIG. 3A  is a front view showing the treatment element  60  in an open state, and  FIG. 3B  is a front view showing the treatment element  60  in a closed state. 
     As shown in  FIGS. 3A and 3B , the treatment element  60  according to this embodiment includes a first scissor piece  61  and a second scissor piece  62  configured to open and close with respect to each other about a first pin  65 . 
     The operating wire  30  slidably inserted through the flexible tube  50  is connected to the base portion  66  of the treatment element  60 . When the operating wire  30  is pushed toward the distal side (to the left in  FIGS. 3A and 3B ), a second pin  64  is biased toward the first pin  65 , so that a linkage mechanism  63  causes the treatment element  60  to open. 
     The linkage mechanism  63  is a four-bar linkage mechanism including a first link plate  611  formed in the base portion of the first scissor piece  61  and a second link plate  621  formed in the base portion of the second scissor piece  62 . 
     Upon pushing the operating wire  30  toward the distal side the first scissor piece  61  and the second scissor piece  62  pivot with respect to each other thus to open as shown in  FIG. 3A . 
       FIG. 3A  illustrates a state where the first scissor piece  61  and the second scissor piece  62  are opened to a maximum angle. When the operating wire  30  is continuously moved forward, an upper limit of the opening angle of the first scissor piece  61  and the second scissor piece  62  is delimited by the maximum open state. 
     Upon pulling the operating wire  30  to the proximal side (to the right in  FIGS. 3A and 3B ), the respective tip portions of the first scissor piece  61  and the second scissor piece  62  are closed by the action of the linkage mechanism  63 , as shown in  FIG. 3B . 
     As shown in  FIGS. 1 and 2 , the main body  22  includes a high-frequency inlet  226  electrically connected to the high-frequency cable  70 . The high-frequency inlet  226  includes a power source terminal  227  to which the high-frequency cable  70  is to be attached. The power source terminal  227  is disposed so as to project in a direction orthogonal to the axis of the high-frequency treatment instrument  10 . 
     Accordingly, the high-frequency cable  70  is connected to the main body  22  in a direction intersecting with the axial line. 
     In the high-frequency treatment instrument  10  according to this embodiment, the high-frequency inlet  226  is fixed to the main body  22 . Upon connecting the high-frequency cable  70  (see  FIG. 2 ) to the high-frequency inlet  226 , the high-frequency cable  70  hangs down from the high-frequency inlet  226  because of its self weight. Accordingly, the rotational manipulator  24  and the operator can be prevented from getting tangled with the high-frequency cable  70 , when the rotational manipulator  24  is operated so as to rotate the treatment element  60 . 
     The axial manipulator  26  according to this embodiment has an axially symmetrical shape. The axial manipulator  26  is rotationally symmetrical about the axial line, and more specifically of a cylindrical shape with a recess circumferentially formed about the axial line that allows the operator to hold the axial manipulator  26  with the forefinger and middle finger. The axial manipulator  26  also includes a pair of flange portions  261  respectively formed on the proximal and distal sides thereof so as to radially protrude outwardly. 
     The high-frequency treatment instrument  10  according to this embodiment also includes an annular auxiliary ring  262  that can be rotated with respect to the main body  22  about the axis. The auxiliary ring  262  includes an opening extending in a direction intersecting with the axial line. The axial manipulator  26  is slidable back and forth but fixed to the main body  22  in terms of rotating motion. 
     The auxiliary ring  262  serves to assist the movement of the axial manipulator  26 , as a fulcrum for sliding the axial manipulator  26  back and forth. 
     The auxiliary ring  262  is pivotally connected to the shaft  228  via a pivotal base  264 . The operator can, for example, insert the thumb through the auxiliary ring  262  and use the forefinger and middle finger to axially slide the axial manipulator  26 , to thereby move the operating wire  30  back and forth. 
     In the high-frequency treatment instrument  10  according to this embodiment, the auxiliary ring  262  is pivotable with respect to the main body  22 , and the axial manipulator  26  has an axially symmetrical shape. Such a configuration allows the operator to hold the high-frequency treatment instrument  10  from any desired direction. 
     Regarding the high-frequency treatment instrument according to the patent document 2, since the holding orientation of the manipulating unit is specifically determined, it may be difficult to perform a rotational or back-and-forth operation depending on the posture of the operator. In addition, in the case of the high-frequency treatment instrument according to the patent document 2, since the treatment element is made to rotate upon rotating the manipulating unit about its axis, the treatment element may accidentally rotate during the operation of the manipulating unit. 
     In contrast, with the high-frequency treatment instrument  10  according to this embodiment, the treatment element  60  can be kept from rotating while the manipulating unit  20  is being handled, unless the rotational manipulator  24  is rotated. Further, since the axial manipulator  26  is accessible from a desired direction, the treatment element  60  can be made to rotate or move back and forth irrespective of the posture of the operator. 
       FIG. 4A  is a vertical cross-sectional view of the manipulating unit  20  according to this embodiment, and  FIG. 4B  is a transverse cross-sectional view thereof.  FIG. 4B  may also be taken as a vertical cross-sectional view of the manipulating unit  20  placed with the lateral side oriented upward. Here, the “vertical cross-section” of the manipulating unit  20  refers to a cross-section taken along a plane containing the axial line of the manipulating unit  20 . In addition,  FIG. 4B  is a cross-sectional view taken along a line IV-IV in  FIG. 2 . 
       FIG. 5  is an enlarged view of a portion around the high-frequency inlet  226  in  FIG. 4A . 
       FIG. 6  is a cross-sectional view of a fitting base  222  formed on the main body  22 . 
     The manipulating unit  20  includes a hollow portion at least on the distal side thereof, and the proximal end portion of the operating wire  30  is inserted along the axial center of the hollow portion. 
     Inside the manipulating unit  20 , a lead pipe  34  made of a metal is attached to the outer circumference of the proximal end portion of the operating wire  30 . The operating wire  30  and the lead pipe  34  are electrically and mechanically connected to each other. Thus, the operating wire  30  and the lead pipe  34  rotate about the axis interlocked with each other. 
     The lead pipe  34  is formed of a conductive metal. The thickness and outer diameter of the lead pipe  34  are not specifically limited. The lead pipe  34  attached to the outer circumference of the operating wire  30  serves to increase the torsional rigidity of the operating wire  30 . 
     The rotational manipulator  24  according to this embodiment is composed of a combination of a cap  247 , an engaging portion  248 , and a base fitting portion  249 , all of which are made of an insulative material. 
     The cap  247  is the portion to be manipulated by the operator, attached to the distal side of the main body  22 . 
     The cap  247  has a generally hemispherical shape, and includes an orifice formed at a position corresponding to the axial center, through which the operating wire  30 , the lead pipe  34  and the flexible tube  50  are inserted. The proximal end portion of the flexible tube  50  is fixed to the cap  247 . 
     The base fitting portion  249  is a cylindrical member, having its proximal end attached to the main body  22  and its distal end coupled with the cap  247 . In other words, the base fitting portion  249  serves as a fixing member that fixes the rotational manipulator  24  to the main body  22 . 
     The base fitting portion  249  includes an opening of an increased diameter formed on the distal side, and a stepped cylindrical projection  244  of a reduced diameter formed on the proximal side. 
     The cap  247  includes a plurality of nail portions  246  formed at different positions on the outer periphery thereof. The nail portions  246  are engaged with the base fitting portion  249 . Accordingly, the cap  247  and the base fitting portion  249  are restricted from moving relatively to each other, both in rotational and sliding motions. 
     The engaging portion  248  is accommodated inside the opening on the distal side of the base fitting portion  249  so as to rotate about the axis together with the cap  247  and the base fitting portion  249 . 
     The engaging portion  248  accommodated inside the opening of the base fitting portion  249  is restricted from rotating about the axis with respect to the base fitting portion  249 . 
     The engaging portion  248  includes a slit  2481  formed so as to axially extend, and hence has a channel shape having a U-shaped cross-section. The engaging portion  248  is attached to the lead pipe  34  from a radial direction. 
     The slit  2481  is formed in an upper region of the axial center of the engaging portion  248 , according to the orientation of  FIG. 4A . In other words, the opening of the U-shaped engaging portion  248  is directed upward in  FIG. 4A . 
     The engaging portion  248  is engaged with the lead pipe  34  so as to apply a rotational torque thereto, and to cause the lead pipe  34  to axially slide. 
     In this embodiment, the lead pipe  34  includes an operating wire engaging portion  37  of a rectangular column shape formed so as to swell from the outer circumferential surface thereof, at a position inside the engaging portion  248 . 
     The width of the slit  2481  of the engaging portion  248  is wider than the distance between opposite faces of the rectangular cross-section of the operating wire engaging portion  37 , i.e., the width of the operating wire engaging portion  37 , but smaller than the diagonal distance of the rectangular cross-section of the operating wire engaging portion  37 . 
     Therefore, when the engaging portion  248  is rotated about the axis with the operating wire engaging portion  37  accommodated inside the slit  2481 , the lead pipe  34  is caused to rotate about the axis. 
     A cylindrical connection cap  230  having an opening on the distal side is provided on the distal side of the main body  22 . The connection cap  230  includes an inner flange  231  formed at the base portion thereof. 
     Through an opening  232  (see  FIG. 6 ) defined by the inner flange  231 , the projection  244  of the base fitting portion  249  is inserted. 
     The high-frequency inlet  226  and the power source terminal  227  are provided on the main body  22  so as to radially protrude therefrom. A power supply terminal  229  electrically connected to the power source terminal  227  is accommodated inside the main body  22 . The power supply terminal  229  and the power source terminal  227  are electrically and mechanically connected to each other, by means of a metal screw (not shown). 
     The main body  22  contains thereinside a conductive pipe  221  made of a metal. The conductive pipe  221  is electrically connected to the high-frequency cable  70  (see  FIG. 2 ), and the operating wire  30  is inserted through the conductive pipe  221 . 
     A cylindrical conductor  32  that slides with respect to the conductive pipe  221  in electrical connection therewith is provided on the operating wire  30 . 
     The conductor  32  is provided on the outer surface of the lead pipe  34 , so as to slidably contact the inner surface of the conductive pipe  221 . 
     A high-frequency current supplied to the power source terminal  227  through the high-frequency cable  70  is applied to the treatment element  60  through the conductive pipe  221 , the conductor  32 , the lead pipe  34 , and the operating wire  30  (see  FIG. 2 ). 
     In the high-frequency treatment instrument  10  according to this embodiment, the conductor  32  and the conductive pipe  221 , both made of a conductive metal material, are slidably disposed and electrically connected to each other. Thus, in the high-frequency treatment instrument  10  according to this embodiment, the power source terminal  227  and the operating wire  30  are electrically connected to each other, substantially free from frictional connection. Accordingly, excellent conductivity can be achieved between the power source terminal  227  and the operating wire  30 , without the need to apply an excessive axial force to push or pull the operating wire  30  with the axial manipulator  26 . 
     As shown in  FIGS. 4A and 4B , an operating wire fixing base  36  is provided at the proximal end portion of the lead pipe  34 , in an expanded shape. The operating wire fixing base  36  is engaged with the axial manipulator  26  so as to rotate about the axis. When axial manipulator  26  is made to slide with respect to the shaft  228 , the lead pipe  34  and hence the operating wire  30  are caused to move back and forth. 
     The shaft  228  includes a slit  225  formed so as to axially extend. 
     The axial manipulator  26  according to this embodiment is composed of a combination of a slider fixer  266  fitted in the slit  225  so as to axially slide with respect to the shaft  228 , and a slider  265  attached to the outer periphery of the slider fixer  266 . The operating wire fixing base  36  is buried in the slider fixer  266 . 
     As shown in  FIG. 5 , a plurality of stepped portions  241 ,  242  is formed on the base portion of the rotational manipulator  24  (base fitting portion  249 ). 
     On the distal side of the main body  22 , on the other hand, inner flange  231  of the connection cap  230 , a stopper  224 , and the power supply terminal  229  constitute a multiple-stage fitting base  222  including a plurality of stepped portions, to which the rotational manipulator  24  is fitted, as indicated by bold lines in  FIG. 6 . 
     Thus, upon fitting the projection  244  of the base fitting portion  249  to the main body  22 , the plurality of stepped portions  241 ,  242  are brought into plane-to-plane contacts with the fitting base  222 . 
     The projection  244  formed at the base portion of the rotational manipulator  24  (base fitting portion  249 ) is inserted through the fitting base  222 . On the other hand, the stopper  224  is located around the projection  244 . The stopper  224  serves to prevent the projection  244  inserted through the fitting base  222  from coming off from the fitting base  222 . 
     The stopper  224  according to this embodiment has a U-shaped cross-section, and serves as a key member to be fitted in a recess  243  formed around the projection  244 . 
     Accordingly, as shown in  FIG. 5 , when the projection  244  of the rotational manipulator  24  is inserted from the distal side through the opening  232  (see  FIG. 6 ) of the main body  22 , the stopper  244  is fitted in a radial direction to the recess  243  of the projection  244 . The stopper  224  is larger in diameter than the opening  232 , and hence inhibits the projection  244  from moving back and forth like a latch. Consequently, the base fitting portion  249  attached to the main body  22  is prevented from being removed to the distal side. 
     The stopper  224  biases the rotational manipulator  24  (base fitting portion  249 ) toward the main body  22 , to the proximal side. Upon fitting the stopper  224  to the recess  243  of the base fitting portion  249 , the stepped portions  241 ,  242  of the base fitting portion  249  are in contact with the fitting base  222  of the stepped shape with a predetermined axial force (normal force). Accordingly, the base fitting portion  249  and the main body  22  are connected so as to rotate relatively to each other, with a predetermined static friction force. 
     With the high-frequency treatment instrument  10  configured as above according to this embodiment, the orientation of the treatment element  60  can be prevented from accidentally fluctuating while moving the operating wire  30  with the controlling axial manipulator  26  or handling the manipulating unit  20 . 
     When the operating wire  30  is made to rotate about the axis by rotating the rotational manipulator  24 , only a part of the rotational angle achieved by the operating wire  30  through the rotational manipulator  24  is transmitted to the treatment element  60 , because of a friction loss between the flexible tube  50  and the operating wire  30 . In other words, when the treatment element  60  is oriented to a desired direction by operating the rotational manipulator  24 , the operating wire  30  set immobile inside the flexible tube  50  is subjected to a predetermined torque. 
     When the axial manipulator  26  is made to slide toward the proximal side of the high-frequency treatment instrument  10  so as to pull the operating wire  30  in this state, the torsional rigidity of the operating wire  30  is improved in proportion to the tension applied thereto. Accordingly, when the operating wire  30  is pulled the operating wire  30  may reversely rotate in the flexible tube  50 , and hence the treatment element  60  may shift from the desired orientation. 
     In the high-frequency treatment instrument  10  according to this embodiment, however, the rotational manipulator  24  and the main body  22  are in contact with each other via the plurality of stepped portions  241 ,  242 , thus engaged with each other with a predetermined friction force. Accordingly, the rotational manipulator  24  and the main body  22  are kept from rotating relatively to each other by the static friction force when the axial manipulator  26  is made to slide so as to pull the operating wire  30 , and therefore the operating wire  30  is prevented from reversely rotating. Consequently, the high-frequency treatment instrument  10  according to this embodiment can prevent the treatment element  60  from shifting from the desired orientation at the moment of performing a treatment such as resection of a diseased part by operating the axial manipulator  26 . 
     Second Embodiment 
       FIGS. 7A to 7C  are cross-sectional views of the manipulating unit  20  of the high-frequency treatment instrument  10  according to a second embodiment.  FIG. 7A  shows a state where the slider  265  is at a retreated position,  FIG. 7B  shows a state where the slider  265  is at the forwardmost position, and  FIG. 7C  shows a state where the operating wire  30  is slacked. 
       FIGS. 8A and 8B  constitute a two-view drawing of a holder  82  constituting a mitigator  80 .  FIG. 8A  is a side view of the distal side of the holder  82 , and  FIG. 8B  is a front view thereof. 
     The high-frequency treatment instrument  10  according to this embodiment further includes a mitigator  80  that applies a biasing force to the operating wire  30  that has axially moved, in an opposite axial direction. 
     In this embodiment, the expression “mitigator  80  applies a biasing force to the operating wire  30 ” is not limited to the case where the mitigator  80  and the operating wire  30  make direct contact with each other so as to transmit the biasing force. This embodiment also encompasses the case where the biasing force is indirectly transmitted from the mitigator  80  to the operating wire  30  through other components such as the slider fixer  266 . 
     The high-frequency treatment instrument  10  according to this embodiment is distinctive in that the tension applied to the operating wire  30  through the operation of the axial manipulator  26  is alleviated by the mitigator  80 . Such an arrangement contributes to improving the operability of the rotational manipulator  24  in the state where the operating wire  30  has been moved forward or backward. As stated above, when the slider  265  is moved so as to axially extend or compress the operating wire  30 , the torsional rigidity of the operating wire  30  increases the greater the tension applied thereto is. Therefore, biasing the operating wire  30  in a direction opposite to the moving direction of the axial manipulator  26  mitigates the tension, so that the natural torsional rigidity of the operating wire  30  can be restored. Such an arrangement prevents the torque necessary for operating the rotational manipulator  24  from excessively increasing. 
     Here, the tension of the operating wire  30  refers to both of the compressing force and the tensile force applied to the operating wire  30 , in this embodiment. 
     As stated with reference to the first embodiment, the high-frequency treatment instrument  10  allows the treatment element  60  to be manipulated free from an impact of the self weight of the high-frequency cable  70 , because of the configuration in which the axial manipulator  26  and the rotational manipulator  24  are provided independently from the main body  22  (see  FIG. 1 ). Employing further the mitigator  80  to thereby alleviate the tension of the operating wire  30  upon moving the same forward or backward according to this embodiment allows the rotational torque necessary for rotating the treatment element  60  to be reduced, thus further improving the operability of the rotational manipulator  24 . 
     Such an advantage can be prominently appreciated, in particular, in the case where the treatment element  60  is opened and its angle is adjusted to the diseased part, which is a typical procedure with a scissors type instrument or a snare instrument. In this embodiment, the treatment element  60  is exemplified by the scissors type element (see  FIGS. 3A and 3B ). 
     The treatment element  60  according to this embodiment includes a plurality of scissor pieces (first scissor piece  61  and second scissor piece  62 ) configured to open and close with respect to each other by moving the operating wire  30  back and forth with the axial manipulator  26 . 
     The mitigator  80  applies a biasing force to the operating wire  30  in a backward or forward direction, when the operating wire  30  is moved forward or backward so that the first scissor piece  61  and the second scissor piece  62  are open from each other. 
     More specifically, the operating wire  30  is pulled toward the proximal side when the slider  265  is at the retreated position as shown in  FIG. 7A , the first scissor piece  61  and the second scissor piece  62  are closed (see  FIG. 3B ). 
     When the slider  265  is moved forward, the operating wire  30  is pushed toward the distal side. With such a movement, the first scissor piece  61  and the second scissor piece  62  pivot about the first pin  65 , so as to present an open state (see  FIG. 3A ). 
     Here, the scissors type treatment element  60  may be a parallel slide type in which the first scissor piece  61  and the second scissor piece  62  move toward and away from each other in a radial direction of the flexible tube  50  maintaining a parallel orientation, instead of the pivotal type as shown in  FIGS. 3A and 3B . 
       FIG. 3A  and  FIG. 7B  illustrate a state where the operating wire  30  has been moved all the way so that the first scissor piece  61  and the second scissor piece  62  are open from each other to the maximum angle. 
     Then as shown in  FIG. 7C , the operating wire  30  is moved backward or forward (in this embodiment, backward) by the biasing force of the mitigator  80  after the maximum open state of the treatment element  60 , so that the first scissor piece  61  and the second scissor piece  62  present an intermediate open state (not shown) in which the aperture (opening angle) is decreased from the maximum open state. Here, the intermediate open state of the treatment element  60  refers to any state other than the maximum open state and a completely closed state. 
     Referring to  FIGS. 7A to 7C ,  FIGS. 8A and 8B , the high-frequency treatment instrument  10  according to this embodiment will be described in further details. 
     The mitigator  80  is composed of a combination of a holder  82  having a channel-shaped vertical cross-section with the opening oriented to a lateral side, and a biasing spring  84 . The mitigator  80  may be composed of a plurality of parts as in this embodiment, or may be formed of a single-piece material. 
     The biasing spring  84  is a helical spring. The outer diameter of the biasing spring  84  is smaller than the opening width of the slit  225  of the main body  22 . The biasing spring  84  is attached around the lead pipe  34 , and elastically extends and contracts in the extending direction of the lead pipe  34 , i.e., the axial direction of the manipulating unit  20  (left and right in  FIGS. 7A to 7C ). 
     The base end portion  841  of the biasing spring  84  may be fixed to the lead pipe  34  or the slider fixer  266 , or unconnected to each other. 
     The holder  82  serves to axially compress the biasing spring  84  to thereby bias the axial manipulator  26  so as to move away from the main body  22 , when the axial manipulator  26  and the main body  22  come axially closer to each other than a predetermined distance. 
     The holder  82  includes a flat pressing surface  821  on the front side thereof oriented toward the distal side of the manipulating unit  20  (left side in  FIG. 8B ), and an opening  822  on the rear side (right side in  FIG. 8B ). A pair of elastic pieces  823  formed generally parallel to each other across the opening  822  each include an latch nail  824  formed so as to outwardly protrude in a vertical direction. The slope angle of the latch nail  824  on the side of the opening (rear side) is milder than the slope angle thereof on the front side. 
     A tapered portion  826  is formed on the inner surface of the rear end portion of the elastic piece  823 , such that the diameter of the opening  822  increases toward the proximal side. 
     The holder  82  includes a groove  825  having an opening oriented downward. The width of the groove  825  is wider than the outer diameter of the lead pipe  34 , and smaller than the outer diameter of the biasing spring  84 . 
       FIG. 9A  is a vertical cross-sectional view showing a state where the mitigator  80  (holder  82  and biasing spring  84 ) is about to be fitted, and  FIG. 9B  is a vertical cross-sectional view showing a state where the mitigator  80  has been fitted. In  FIG. 9A , dash-dot-dot lines show the holder  82  in the natural state, and solid lines show the holder  82  with the latch nail  824  insert-fitted. 
       FIGS. 9A and 9B  illustrate the slider fixer  266 , the operating wire fixing base  36  buried in the slider fixer  266 , the lead pipe  34  extending toward the distal side from the operating wire fixing base  36 , and the operating wire  30  inserted through the lead pipe  34 . The slider  265  and the main body  22  are not shown. 
     First, the biasing spring  84  is attached from the distal side (left in  FIG. 9A ) of the lead pipe  34 . The biasing spring  84  is attached so as to slide with respect to the lead pipe  34 . 
     Then the lead pipe  34  is inserted in the groove  825  with the pressing surface  821  of the holder  82  oriented toward the distal side. At this stage, the holder  82  is located so as to straddle on the lead pipe  34  as shown in  FIG. 9A . 
     Thereafter, the elastic pieces  823  of the holder  82  are pressed in a vertical direction such that the latch nails  824  sink with respect to the pressing surface  821 , and the holder  82  is inserted between a pair of arms  267  of the slider fixer  266 . At this moment, since the opening side (rear side) of the latch nail  824  is gently inclined, the latch nails  824  are biased toward the axial center by the front end portion  268  of the slider fixer  266  simply by pressing the holder  82  to the rear side, and the elastic pieces  823  are inwardly deflected. Thus, the latch nails  824  become able to pass between the pair of front end portions  268 . 
     Here, since the elastic piece  823  includes the tapered portion  826  formed on the inner surface of the rear end portion, the tapered portion  826  becomes parallel to the lead pipe  34  when the elastic piece  823  is deflected, as shown in  FIG. 9A . At this moment, the distance between the tapered portions  826  is larger than the outer diameter of the biasing spring  84 , and therefore the holder  82  can intrude through between the arms  267  along the outer periphery of the biasing spring  84 . 
     As shown in  FIGS. 9A and 9B , a stepped portion  269  is provided between the front end portion  268  and the arm  267  of the slider fixer  266 . When the latch nail  824  passes the stepped portion  269 , the latch nails  824  again protrude with respect to the pressing surface  821  because of the elastic restoring force of the elastic piece  823 , as shown in  FIG. 9B . Thus, the latch nail  824  and the stepped portion  269  are engaged with each other, so that holder  82  is restricted from coming off from the slider fixer  266 . 
     Through the foregoing procedure, the holder  82  and the biasing spring  84  can be fitted inside the slider fixer  266 . 
     Referring again to  FIGS. 7A to 7C , the working of the mitigator  80  according to this embodiment will be described in details. 
     The holder  82  and the biasing spring  84  are accommodated in the slit  225  of the manipulating unit  20 , and fitted inside the slider fixer  266 . 
     On the other hand, the main body  22  includes a backward projection  223  formed so as to axially protrude from the distal side of the axial manipulator  26  toward the inside of the slit  225 . The backward projection  223  has a tapered shape such that the width thereof decreases toward the proximal side. The proximal side end face of the backward projection  223  is flat and parallel to the pressing surface  821  of the holder  82 . 
     As shown in  FIG. 7A , the holder  82  and the biasing spring  84  are located between the main body  22  and the axial manipulator  26 . In other words, the mitigator  80  (holder  82  and biasing spring  84 ) is resiliently interposed between the main body  22  and the axial manipulator  26 . 
     When the slider  265  is at the retreated position as shown in  FIG. 7A , the biasing spring  84  assumes its natural length and hence the main body  22  and the axial manipulator  26  are not subjected to a biasing force. 
     Also, the first scissor piece  61  and the second scissor piece  62  of the treatment element  60  are closed, as stated above (see  FIG. 3B ). The treatment element  60  and the flexible tube  50  are inserted through a forceps channel of an endoscope (not shown) in this state. 
     Here, an endoscope normally includes a plurality of forceps channels. In the forceps channels, optical systems such as a fiber scope and a charge-coupled device (CCD) camera are inserted, in addition to the high-frequency treatment instrument  10  according to this embodiment. In addition, a cylindrical hood may be attached to the distal end portion of the endoscope. Attaching the hood to the distal end portion of the endoscope so as to protrude therefrom allows the relative position between a diseased part and the optical system to be fixed while maintaining unchanged the distance therebetween. 
     When the treatment element  60  sticks out from the distal end portion of the forceps channel of the endoscope, the position and rotational angle of the treatment element  60  inside the hood can be monitored through the optical system. Then the rotational manipulator  24  is rotated about the axis so as to adjust the rotational angle of the treatment element  60  to the diseased part, monitoring the treatment element  60  through the optical system. A specific example of the manipulation of the treatment element  60  will be described here below. 
     First, the operator passes a first finger (thumb) through the auxiliary ring  262  (see  FIG. 1 ), and holds the slider  265  with other fingers to move the axial manipulator  26  forward all the way through its stroke range, as shown in  FIG. 7B . Such a state will be herein referred to as forwardmost position of the axial manipulator  26 . 
     In the forwardmost position of the axial manipulator  26 , the operating wire  30  is moved forward with the axial manipulator  26 , so that the first scissor piece  61  and the second scissor piece  62  present the maximum open state (see  FIG. 3A ). Accordingly, the V-shape formed by the first scissor piece  61  and the second scissor piece  62  can be monitored through the optical system. 
     In the case where the treatment element  60  is of a scissors type, a widthwise size (vertical direction in  FIG. 3B ) and a thicknesswise size (depthwise direction in  FIG. 3B ) are close when the scissors are closed, and therefore it is generally difficult to visually recognize the rotational angle of the treatment element  60  through the optical system. Accordingly, it is preferable to monitor the rotational angle through the optical system with the treatment element  60  opened, as in this embodiment. 
     At this stage, the holder  82  is pressed to the proximal side (to the right in  FIG. 7B ) by the backward projection  223 , and the elastic pieces  823  are made to abut against the slider fixer  266 . Since the natural length of the biasing spring  84  is longer than the elastic piece  823 , the biasing spring  84  is elastically compressed when the holder  82  is pressed deeper into the slider fixer  266 . Accordingly, the biasing spring  84  exerts an axially backward biasing force on the operating wire  30  through the slider fixer  266  and the lead pipe  34 . However, as long as the fingers of the operator hold the axial manipulator  26 , the axial manipulator  26  stays immobile at the forwardmost position, and the biasing spring  84  remains compressed. 
     When the operator releases the axial manipulator  26  from the fingers, the biasing spring  84  causes the holder  82  and the slider fixer  266  to slide so as to move away from each other, with an elastic restoring force. Thus the slider fixer  266  is moved backward as shown in  FIG. 7C . 
     Here, the elastic restoring force gained by the biasing spring  84  when the axial manipulator  26  is at the forwardmost position is greater than the total of a maximum static friction force between the operating wire  30  and lead pipe  34  and slider fixer  266 , and the flexible tube  50  and main body  22 . Therefore, when the operator simply releases the axial manipulator  26  from the fingers, the axial manipulator  26  slightly moves backward. 
     Then the tensile force (compressive force) of the operating wire  30  pressed to the forwardmost position is at least partially offset, so that the operating wire  30  becomes substantially slacked. 
     In this embodiment, the state where the axial manipulator  26  is at an intermediate position other than the forwardmost and the backwardmost position of the stroke range will be referred to as slacked state of the operating wire  30 . 
     In the slacked state of the operating wire  30  shown in  FIG. 7C , since the first scissor piece  61  and the second scissor piece  62  (see  FIG. 3A ) are open from each other, the orientation of the treatment element  60  can be monitored through the optical system. In addition, the aperture between the first scissor piece  61  and the second scissor piece  62  in the slacked state of the operating wire  30  is smaller than the aperture in the maximum open state. Therefore, the tip portions of the first scissor piece  61  and the second scissor piece  62  can be prevented from interfering with the inner surface of the hood. 
     As described above, with the high-frequency treatment instrument  10  according to this embodiment, although the operator moves the axial manipulator  26  all the way to the forwardmost position, the aperture of the treatment element  60  automatically decreases so that the operating wire  30  is slacked, when the operator only releases the axial manipulator  26  from the fingers. Accordingly, when the operator proceeds to the operation of the rotational manipulator  24  the tension of the operating wire  30  is mitigated, and therefore the operator can smoothly operate the rotational manipulator  24  without the need to apply a large rotational torque. Further, since the treatment element  60  is in the intermediate open state when the rotational manipulator  24  is about to be operated, the treatment element  60  can be prevented from physically interfering with the hood without compromise in visibility through the optical system. 
     In particular, in the case where the axial manipulator  26  has a large stroke range such that the axial manipulator  26  can still move forward even after the treatment element  60  reaches the maximum open state, a large amount of compressive force may be imposed to the operating wire  30  upon moving the axial manipulator  26  further forward. However, by utilizing the mitigator  80  so as to mitigate or eliminate the compressive force against the operating wire  30  as in this embodiment, the rotational torque necessary for operating the rotational manipulator  24  can be significantly minimized. 
       FIGS. 10A to 10C  are cross-sectional views showing a variation of the high-frequency treatment instrument  10  according to the second embodiment. In the high-frequency treatment instrument  10  according to this variation, the mitigator  80  includes the holder  82  engaged with the operating wire  30  with a predetermined engaging force so as to restrict the back-and-forth movement of the axial manipulator  26 , and a biasing member (biasing spring  84 ) resiliently interposed between the holder  82  and the axial manipulator  26 . In the high-frequency treatment instrument  10  according to this variation, the holder  82  and the operating wire  30  are disengaged from each other thus allowing the axial manipulator  26  to axially move, in the case where a load greater than a predetermined engaging force is axially imposed on the axial manipulator  26 . 
     The holder  82  is directly or indirectly engaged with the operating wire  30 . In this variation, the holder  82  is fitted to the lead pipe  34  through which the operating wire  30  is inserted, and the holder  82  frictionally slides with respect to the lead pipe  34 .  FIG. 10A  shows a state where the axial manipulator  26  is restricted from moving forward because of the engagement between the holder  82  and the lead pipe  34  (operating wire  30 ). As shown therein, the holder  82  is engaged with the lead pipe  34  through a static friction force and the biasing spring  84  is compressed, when the axial manipulator  26  starts to move from the retreated position toward the distal side (to the left in  FIG. 10A ). 
     The engagement between the holder  82  and the operating wire  30  may be achieved by friction as described above, or by a projection and recess that can be engaged or disengaged by a predetermined axial external force. 
     As the axial manipulator  26  moves further forward, the compression amount of the biasing spring  84  increases. When the elastic restoring force of the biasing spring  84  is balanced with the maximum static friction force between the holder  82  and the lead pipe  34 , the holder  82  frictionally slides with respect to the lead pipe  34  toward the distal side, as shown in  FIG. 10B .  FIG. 10B  illustrates how the axial manipulator  26  is moving forward. 
     The pressing surface  821  of the holder  82  according to this variation protrudes to the distal side with respect to the front end portion  268  of the slider fixer  266 , when the holder  82  is pressed to the deepest position between the arms  267  of the slider fixer  266  (see  FIGS. 9A and 9B ). 
     When the axial manipulator  26  moves further forward from the state shown in  FIG. 10B  and the pressing surface  821  of the holder  82  is brought into contact with the main body  22 , the biasing spring  84  exerts an elastic force toward the proximal side on the slider fixer  266  (see  FIG. 10C ). 
     Accordingly, the axial manipulator  26  is moved slightly backward from the forwardmost position, so that apart of the pressing force against the operating wire  30  is removed and the operating wire  30  becomes slacked.  FIG. 10C  therefore illustrates the slacked state of the operating wire  30 . At this moment, the first scissor piece  61  and the second scissor piece  62  (see  FIG. 3A ) slightly reduces the aperture from the maximum open state. Therefore, the rotational torque necessary for operating the rotational manipulator  24  is reduced, and physical interference between the treatment element  60  (see  FIG. 1 ) and the hood can be avoided. 
     The high-frequency treatment instrument  10  offers a unique and prominent advantage when used for a body cavity that is curved or bent (hereinafter simply defined as curved without strict distinction therebetween). 
     In the case where the body cavity (or lumen of a catheter inserted therethrough) is curved, when the flexible tube  50  and the operating wire  30  of the high-frequency treatment instrument  10  (hereinafter, see  FIG. 1 ) are inserted the operating wire  30  advances relatively to the flexible tube  50 . This is because the operating wire  30  inserted through the flexible tube  50  moves over a longer path length than the inner side of the curved portion of the flexible tube  50 . Accordingly, as the flexible tube  50  and the operating wire  30  are further curved, the operating wire  30  advances with respect to the flexible tube  50  while the treatment element  60  at the distal end portion of the flexible tube  50  remains closed, and the axial manipulator  26  is drawn toward the distal side. 
     In contrast, with the high-frequency treatment instrument  10  according to this variation, although the axial manipulator  26  is slightly drawn toward the distal side so that the biasing spring  84  is compressed, the holder  82  frictionally engaged with the lead pipe  34  serves as a stopper so as to restrict the axial manipulator  26  from moving forward, as shown in  FIG. 10A . Therefore, with the high-frequency treatment instrument  10  according to this variation, the axial manipulator  26  is kept from moving all the way to the tip position of the slit  225 , even though the flexible tube  50  and the operating wire  30  are inserted in a curved body cavity or lumen. In other words, the maximum static friction force constituting the engaging force between the holder  82  and the lead pipe  34  is greater than the elastic restoring force of the biasing spring  84  generated at the advanced position of the axial manipulator  26  in the case where the flexible tube  50  and the operating wire  30  are curved. 
     Thus, even in the case where the high-frequency treatment instrument  10  is inserted in a curved body cavity or lumen and the treatment element  60  has reached the vicinity of the diseased part, a surplus for further forward stroke is still left available for the axial manipulator  26  so as to open the treatment element  60 . 
     However, the external force exerted by the operator to move the axial manipulator  26  forward is by far greater than the engaging force between the holder  82  and the lead pipe  34 . Accordingly, as shown in  FIG. 10B , upon moving the axial manipulator  26  forward, the holder  82  moves forward with the slider fixer  266  with respect to the lead pipe  34 . Therefore the operating wire  30  advances relatively to the main flexible tube  50  fixed to the body  22 , so that the treatment element  60  is opened. 
     In the case where the axial manipulator  26  has reached the forwardmost position, the axial manipulator  26  is moved slightly backward by the resilient force of the biasing spring  84  as shown in  FIG. 10C , and the operating wire  30  becomes slacked as stated above. 
     Thus, with the high-frequency treatment instrument  10  according to this variation, even though the flexible tube  50  is inserted in a curved body cavity or lumen, the mitigator  80  properly restricts the forward movement of the axial manipulator  26 , so that the axial manipulator  26  and the mitigator  80  can fully perform the respective functions. 
     This application claims priority based on Japanese Patent Application No. 2009-123077 filed on May 21, 2009, the content of which is incorporated hereinto in its entirety.