A treatment tool includes an elongated shaft that has a bending mechanism at a distal end thereof; a bending operation part that is connected to a proximal-end side of the shaft in order to operate the bending mechanism; a connection sleeve that is provided at a connection section of the bending operation part where the bending operation part and the shaft are connected, and that rotatably holds the shaft; a rotation operation member that is provided at the proximal-end side of the shaft and that rotates the shaft; and a stopper member that can be made to slide outside the connection sleeve along a direction of a longitudinal axis of the shaft and that is engaged with both the rotation operation member and the connection sleeve at a specific position in a range of movement thereof, thereby locking rotation of the shaft with respect to the connection sleeve.