A treatment device includes a longitudinal probe, a distal end portion, a sheath, a fixed handle, a movable handle, a jaw side through hole portion that is provided in the movable handle and formed between a finger placing portion and a jaw, a sheath side through hole portion that is provided in the sheath and provided at a position at which the sheath side through hole portion does not overlap with the hollow portion; and an opening/closing axis member. The opening/closing axis member is inserted in the jaw side through hole portion and the sheath side through hole portion to openably and closably attach the movable handle to the fixed handle.