A treatment instrument for an endoscope used in combination with an endoscope having a raising base at a distal end section of a channel, the treatment instrument for the endoscope comprising: a sheath section having flexibility; a treatment section installed closer to a distal end side than the sheath section; and a manipulation unit installed at a proximal end of the sheath section and configured to manipulate the treatment section, wherein the sheath section includes: a sheath main body having a lumen ( 16, 17, 92) extending along an axis of the sheath section; a sandwiched portion formed at a distal end side of the sheath main body and sandwiched between the raising base being raised and an inner circumferential surface of the channel, an outer diameter of the sandwiched portion being larger than a diameter of a maximum inscribed circle among inscribed circles of portions sandwiching the sandwiched portion between the raising base and the inner circumferential surface of the channel when the raising base is completely raised; and a torque transmission member extending from a proximal end of the sheath main body to the sandwiched portion in an axial direction of the sheath section and configured to transmit a rotational torque input by a user and rotate the sheath main body about the axis, and characterized in that the torque transmission member includes: a tubular, metal blade fitted onto a distal portion of the sheath main body; and a wire in which a distal end of the wire is protruded from a distal end side of the lumen and the distal end of the wire is fixed to the blade, and wherein a proximal end of the wire protruded from a proximal end of the lumen is provided with a grip being configured to be capable of operating to input the rotation torque to the torque transmission member. a sheath section having flexibility; a treatment section installed closer to a distal end side than the sheath section; and a manipulation unit installed at a proximal end of the sheath section and configured to manipulate the treatment section, wherein the sheath section includes: a sheath main body having a lumen ( 16, 17, 92) extending along an axis of the sheath section; a sandwiched portion formed at a distal end side of the sheath main body and sandwiched between the raising base being raised and an inner circumferential surface of the channel, an outer diameter of the sandwiched portion being larger than a diameter of a maximum inscribed circle among inscribed circles of portions sandwiching the sandwiched portion between the raising base and the inner circumferential surface of the channel when the raising base is completely raised; and a torque transmission member extending from a proximal end of the sheath main body to the sandwiched portion in an axial direction of the sheath section and configured to transmit a rotational torque input by a user and rotate the sheath main body about the axis, and characterized in that the torque transmission member includes: a tubular, metal blade fitted onto a distal portion of the sheath main body; and a wire in which a distal end of the wire is protruded from a distal end side of the lumen and the distal end of the wire is fixed to the blade, and wherein a proximal end of the wire protruded from a proximal end of the lumen is provided with a grip being configured to be capable of operating to input the rotation torque to the torque transmission member. a sheath main body having a lumen ( 16, 17, 92) extending along an axis of the sheath section; a sandwiched portion formed at a distal end side of the sheath main body and sandwiched between the raising base being raised and an inner circumferential surface of the channel, an outer diameter of the sandwiched portion being larger than a diameter of a maximum inscribed circle among inscribed circles of portions sandwiching the sandwiched portion between the raising base and the inner circumferential surface of the channel when the raising base is completely raised; and a torque transmission member extending from a proximal end of the sheath main body to the sandwiched portion in an axial direction of the sheath section and configured to transmit a rotational torque input by a user and rotate the sheath main body about the axis, and characterized in that the torque transmission member includes: a tubular, metal blade fitted onto a distal portion of the sheath main body; and a wire in which a distal end of the wire is protruded from a distal end side of the lumen and the distal end of the wire is fixed to the blade, and wherein a proximal end of the wire protruded from a proximal end of the lumen is provided with a grip being configured to be capable of operating to input the rotation torque to the torque transmission member. a tubular, metal blade fitted onto a distal portion of the sheath main body; and a wire in which a distal end of the wire is protruded from a distal end side of the lumen and the distal end of the wire is fixed to the blade, and wherein a proximal end of the wire protruded from a proximal end of the lumen is provided with a grip being configured to be capable of operating to input the rotation torque to the torque transmission member.