A treatment instrument includes: a first treatment section which includes a first body including a first contact surface and a second body including a second contact surface； a movement mechanism which is configured to switch between a closed position in which the first contact surface and the second contact surface are close to each other, and an opened position in which the first contact surface and the second contact surface are distant from each other； and a second treatment section which is disposed on a distal side along the longitudinal axis with respect to the first treatment section when the first contact surface and the second contact surface are located in the closed position, and which is configured to apply energy to the living tissue to incise or separate the living tissue.
