A treatment tool for an endoscope includes a sheath which includes a proximal region, a distal region, an outer circumference surface, and an inner circumference surface; a slit portion which extends from the proximal region to the distal region in the longitudinal axis direction of the sheath and is formed to pierce through the sheath from the inner circumference surface to the outer circumference surface; an inlet portion which includes an opening that is formed at the outer circumference surface in the proximal region, the opening being formed to communicate with the slit portion, and being formed to pierce through the sheath from the inner circumference surface to the outer circumference surface in a same direction with that of the slit portion, and a locking portion which is connected to the sheath to be locked to the endoscope apparatus.