To provide an actuator having a working pin capable of moving the working pin at high speed, and preventing the working pin from returning after working.

This actuator 33 includes an actuator body 34, and the working pin 39 jointed with the actuator body 34. The actuator body 34 includes a squib 35 and a metallic bag 37 which flows expansion gas generated by the squib 35 into the inside, expands while performing plastic deformation so as to keep the shape at the completion timing of expansion, and is jointed with the working pin 39 at a part of the circumferential wall. The metallic bag 37 expands so as to attract the joint part with the working pin 39 toward the center of a bag shape at the completion timing of expansion and so as to movably attract the working pin 39 in an axial direction, thus deploying at least around the joint part with the working pin 39 before working in a flat state.