A medical instrument (1) includes a joint part (10). The joint part (10) has a flexible cladding tube part (11) and a bending tube (12) arranged inside the cladding tube part (11). The bending tube (12) is fixed to an inner surface of the cladding tube (11) at a distal end part (15) thereof, and supports an incision electrode (4) at a proximal end part (13) thereof. The bending tube (12) has a flexible spring part (14) between the proximal end part (15) and the distal end part (13). Distal ends of two wires (24-25) are fixed to the distal end part (13). Proximal ends of the wires (24-25) are pulled by actuators (33-34). When the actuators (33-34) pull only one of the two wires (24-25), the flexible spring part (14) and the cladding tube part (11) bend. When the actuators (33-34) pull both of the two wires (24-25) at the same time, the flexible spring part (14) contracts, and the incision electrode (4) is stored in the cladding tube (11).
