A treatment device (10) includes a probe (3), a sheath (23), a jaw (52) and an opening/closing axis member (100) that has an opening/closing axis (101). The opening/closing axis member (100) is provided at a position offset to the hollow portion (23a) in an opening/closing direction so that the opening/closing axis member does not overlap with the hollow portion (23a) in the opening/closing direction. In a state, the opening/closing axis member (100) is inserted in the jaw (23) and the sheath (52) so that the opening/closing axis member (100) pierces through the sheath (23) and the jaw (52) provided in parallel with each other in an opening/closing axis direction at a position offset to the hollow portion (23) in the opening/closing direction. The opening/closing axis member (100) attaches the jaw (23) to the sheath (52) by the insertion thereof.
