A treatment device includes: a transmitting member moving back and forth along a longitudinal axis of an insertion portion to transmit a drive force to rotate an end effector a first locking portion provided on the proximal side of the transmitting member a second locking portion provided on the proximal side of the insertion portion and configured to engage with the first locking portion and an operational body which activates the first locking portion relative to the second locking portion, which is configured to switch between a first position where the transmitting member is moved forward along the longitudinal axis of the insertion portion to keep the end effector in a first state to extend along the longitudinal axis relative to the distal end of the insertion portion along the longitudinal axis, and a second position where the transmitting member is moved backward along the longitudinal axis of the insertion portion to keep the end effector in a second state to be rotated relative to the longitudinal axis with respect to the distal end of the insertion portion.
