An endoscope treatment system includes an endoscope apparatus which includes a tubular member that is capable of being operated to be bent and a bending operation section that is provided to bend the tubular member, and a treatment tool for an endoscope which is inserted into a treatment tool channel of the endoscope apparatus. The treatment tool for an endoscope includes an insertion portion which is capable of being inserted into a body, and an operation portion which is disposed at a proximal end of the insertion portion. The insertion portion includes a sheath which has an outer diameter so as to allow the sheath to be capable of being inserted into the treatment tool channel, and a knife wire which is disposed on a distal end portion of the sheath and incises tissues. The sheath includes a lumen which has an inner diameter so as to allow a guide wire to be capable of being inserted into the lumen, an outlet portion which is open to a distal end portion of the sheath and communicates with the lumen, and an inlet portion which is open to an outer circumferential surface of a proximal end portion of the sheath. The operation portion includes a port which communicates with the inlet portion and includes a through-hole into which the guide wire is capable of being inserted, and a locking portion which is capable of being locked to the endoscope apparatus such that an opening direction of the through-hole of the port faces the bending operation section side in a state where the insertion portion is inserted into the treatment tool channel.
