An arm member is capable of moving to a first position, a second position, a third position, and a fourth position, in order, by driving a stepping motor in one direction. A shutter blade is in a closed state and a light quantity adjustment blade is in an insertion state when the arm member is at the first position, the shutter blade is in an open state and the light quantity adjustment blade is in the insertion state when the arm member is at the second position, the shutter blade is in the open state and the light quantity adjustment blade is in the evacuation state when the arm member is at the third position, and the shutter blade is in the closed state and the light quantity adjustment blade is in the evacuation state when the arm member is at the fourth position.