A driving force transmitting unit is removably attached to an actuation unit in a cavity when inserted through a channel from an insertion hole, and transmits a rotation driving force to the actuation unit by rotating around a driving axis when attached to the actuation unit. The driving force transmitting unit includes a line portion extending along the driving axis in the channel, a distal connection portion connected to the actuation unit when attached to the actuation unit, and a driving force receiving portion located and set at a position to receive the rotation driving force from a driving source unit when attached to the actuation unit.
