A drive unit (101) includes: a first gear (61) that rotates about a first axis (161)； a second gear (62) that rotates about a second axis (162) extending in a direction perpendicular to the first axis (161)； and a third gear (63) that rotates about a third axis (163) extending in a direction perpendicular to the first axis (161). Elongated elements (13) include: a first elongated element (13a) that is rigid and meshes with the second gear (62)； and a second elongated element (13b) that is rigid and meshes with the third gear (63). The second gear (62) and third gear (63) mesh with the first gear (61). The distal end part (11) is operated in such a manner that as the first gear (61) rotates, the first elongated element (13a) moves in a longitudinal direction of the medical treatment tool (4b) while the second elongated element (13b) moves in a direction opposite to the direction in which the first elongated element (13a) moves.
