A treatment device comprising: an insertion portion which includes a distal end, a proximal end, and a longitudinal axis defined by the distal end and the proximal end; an end effector which is coupled to the distal end of the insertion portion rotatably on a first rotation shaft, wherein said first rotation shaft intersects at a right angle with the longitudinal axis and is located apart from the longitudinal axis; a transmitting member which is coupled to the end effector so that the end effector is rotatable on a second rotation shaft and transmits a drive force of the transmitting member to the end effector to rotate the end effector, wherein said second rotation shaft is parallel to the first rotation shaft and is located opposite to the first rotation shaft across the longitudinal axis, wherein if the transmitting member is moved forward relative to the insertion portion along the longitudinal axis, the end effector is disposed at a first position, and if the transmitting member is moved backward relative to the insertion portion along the longitudinal axis, the end effector is disposed at a second position; a first locking portion (42; 102; 132; 152) which is provided on the proximal side of the transmitting member; a second locking portion (44; 104; 134; 154) which is provided on the proximal side of the insertion portion and which is configured to engage with the first locking portion; and an operational body which is provided on the proximal side of the transmitting member, 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; characterized by further comprising an urging body which is disposed between the second locking portion and the operational body and urges the operational body forward along the longitudinal axis of the insertion portion or which is disposed between the second locking portion and the transmitting member and urges the transmitting member forward along the longitudinal axis of the insertion portion. an insertion portion which includes a distal end, a proximal end, and a longitudinal axis defined by the distal end and the proximal end; an end effector which is coupled to the distal end of the insertion portion rotatably on a first rotation shaft, wherein said first rotation shaft intersects at a right angle with the longitudinal axis and is located apart from the longitudinal axis; a transmitting member which is coupled to the end effector so that the end effector is rotatable on a second rotation shaft and transmits a drive force of the transmitting member to the end effector to rotate the end effector, wherein said second rotation shaft is parallel to the first rotation shaft and is located opposite to the first rotation shaft across the longitudinal axis, wherein if the transmitting member is moved forward relative to the insertion portion along the longitudinal axis, the end effector is disposed at a first position, and if the transmitting member is moved backward relative to the insertion portion along the longitudinal axis, the end effector is disposed at a second position; a first locking portion (42; 102; 132; 152) which is provided on the proximal side of the transmitting member; a second locking portion (44; 104; 134; 154) which is provided on the proximal side of the insertion portion and which is configured to engage with the first locking portion; and an operational body which is provided on the proximal side of the transmitting member, 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; characterized by further comprising an urging body which is disposed between the second locking portion and the operational body and urges the operational body forward along the longitudinal axis of the insertion portion or which is disposed between the second locking portion and the transmitting member and urges the transmitting member forward along the longitudinal axis of the insertion portion.