A bipolar cutter, comprising: an insertion unit configured to be inserted into a body of a living thing; a bipolar cutting treatment portion having a pair of electrodes (48, 50) provided at a front-end portion of the insertion unit; and a guide portion provided in the front-end portion of the insertion unit and having a lead passage configured to capture a living tissue of a cutting target in the body of the living thing, and to lead the living tissue to the bipolar cutting treatment portion, the guide portion being configured to vary a width of the lead passage, wherein the bipolar cutter further comprises a lead passage width variable manipulation portion configured to manipulate the guide portion to vary the width of the lead passage; characterized in that: the guide portion has a pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b), which project from the front-end portion of the insertion unit in parallel along a lengthwise direction of the insertion unit, and which form the lead passage therebetween, at least one of the pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b) is movably provided in a front-end portion of the insertion unit and adapted to vary the width of the lead passage by moving in a direction orthogonal to a lengthwise center line of the insertion unit with inner facing edges of the capturing members in parallel with the lengthwise center line of the insertion unit, one of the pair of electrodes (48, 50) of the bipolar cutting treatment portion covers the facing inner edges of the pair of capturing members (32a, 32b, 32"a, 32"b, 102a, 102b) forming the lead passage, and the other of the pair of electrodes (48, 50) faces the lead passage at the front-end portion of the insertion unit. an insertion unit configured to be inserted into a body of a living thing; a bipolar cutting treatment portion having a pair of electrodes (48, 50) provided at a front-end portion of the insertion unit; and a guide portion provided in the front-end portion of the insertion unit and having a lead passage configured to capture a living tissue of a cutting target in the body of the living thing, and to lead the living tissue to the bipolar cutting treatment portion, the guide portion being configured to vary a width of the lead passage, wherein the bipolar cutter further comprises a lead passage width variable manipulation portion configured to manipulate the guide portion to vary the width of the lead passage; characterized in that: the guide portion has a pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b), which project from the front-end portion of the insertion unit in parallel along a lengthwise direction of the insertion unit, and which form the lead passage therebetween, at least one of the pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b) is movably provided in a front-end portion of the insertion unit and adapted to vary the width of the lead passage by moving in a direction orthogonal to a lengthwise center line of the insertion unit with inner facing edges of the capturing members in parallel with the lengthwise center line of the insertion unit, one of the pair of electrodes (48, 50) of the bipolar cutting treatment portion covers the facing inner edges of the pair of capturing members (32a, 32b, 32"a, 32"b, 102a, 102b) forming the lead passage, and the other of the pair of electrodes (48, 50) faces the lead passage at the front-end portion of the insertion unit. the guide portion has a pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b), which project from the front-end portion of the insertion unit in parallel along a lengthwise direction of the insertion unit, and which form the lead passage therebetween, at least one of the pair of capturing members (32a, 32b, 32a", 32b", 102a, 102b) is movably provided in a front-end portion of the insertion unit and adapted to vary the width of the lead passage by moving in a direction orthogonal to a lengthwise center line of the insertion unit with inner facing edges of the capturing members in parallel with the lengthwise center line of the insertion unit, one of the pair of electrodes (48, 50) of the bipolar cutting treatment portion covers the facing inner edges of the pair of capturing members (32a, 32b, 32"a, 32"b, 102a, 102b) forming the lead passage, and the other of the pair of electrodes (48, 50) faces the lead passage at the front-end portion of the insertion unit.