PURPOSE: To make the design easy, by connecting a coil spring having a connecting rod to an end of a piston rod, supporting the connecting rod to a guide, and supporting the coil spring to a second coil spring.

CONSTITUTION: A coil spring 2 is provided at its one end with a connecting rod 1, and is connected at the other end with an end of a piston rod 3. The connecting rod 1 is supported to a guide 4, and the coil spring 2 is supported to a second coil spring 5. With this arrangement, a cylinder 7 as a driving source may be separated from an end portion required to actually operate, and accordingly, it is not necessary to install the cylinder 7 in a narrow space, thus making the design easy.