To enable a movement in one direction to be continued to an end by applying an external force to a middle part and to use spring energy for a movement in the other direction.

Spring energy is accumulated while a movement member moves to a predetermined position in one direction by an external force. Then, the movement in one direction is continued by a movement force based on a spring force, a gravity force, or a composite force thereof while restricting the release of the accumulated spring energy. The movement from an end position in one direction to an end position in the other direction is made by the accumulated spring energy.