An actuator AE1 includes a lock mechanism R1 configured to fill a gas G generated by operating a gas generator 35 at inside of a cylinder 22 and moving forward a piston 38 along with a support rod 40 for restricting a rearward movement of the support rod moved forward. The support rod 40 is arranged to be able to absorb a kinetic energy of a protection object person and capable of being plastically deformed when the protection object person is received by a receiving member after having been moved forward. A lock mechanism R1 is constituted by a diameter enlarging deformed portion 42 arranged at a piston and a locking stepped portion 24 capable of restricting the rearward movement of the piston. Further, the diameter enlarging deformed portion 42 is locked by the locking stepped portion 24 by being elastically deformed by an elastic force of the diameter enlarging deformed portion 42 per se from a diameter contracting state to a diameter enlarging state when arranged to the locking stepped portion 24 after moving the piston forward.