Included are an output member including a coupling allowed to be engaged with a unit; an input member; an input-side engagement member; an output-side engagement member allowed to be engaged with the input-side engagement member; an elastic member urging the input-side engagement member toward the output-side engagement member; and a disengagement member which moves the input-side engagement member at an engaged position, at which engagement with the output-side engagement member is allowed, to a disengaged position at which engagement with the output-side engagement member is released. In each of a state where the input-side engagement member is at the engaged position and a state where the input-side engagement member is at the disengaged position, a space is formed in which the output-side engagement member is allowed to move in the shaft direction when the output member is pressed to the shaft direction.