In a state wherein an actuator is located at a shunt position, when an apparatus is subjected to an external shock, the actuator tries to swing due to a rotational moment. An inertia arm generates a rotational moment simultaneously with the actuator. Both the rotational moments competes with each other at an engaging point of the inertia arm side with the actuator side to absorb the external shock. Further the actuator tries to excessively swing exceeding the limit of the original swing range during the operation of the apparatus. In order to prevent this, the inertia arm is used.