A procedure of positioning a treatment part at various sites on an organ is facilitated, and the positioning thereof can be stably maintained for treatment with accurate positioning. A treatment instrument (1) includes a rigid rod-shaped insertion section (2) having a treatment part at a distal end thereof and a manipulating section (3) secured to a proximal end of the insertion section (2) and gripped and manipulated by an operator. The insertion section (2) includes a main body (8) extending in a straight line, a first curved portion (9) disposed at a distal end of the main body (8) and curved in one direction with respect to the main body (8), and a second curved portion (10) disposed on a distal side of the first curved portion (9) and curved in a direction opposite to the direction in which the first curved portion (9) is curved. The treatment part is inclined with respect to the longitudinal axis of the main body (8).
