A stopper mechanism includes a second cylinder disposed at an end in a first cylinder, a second piston disposed so as to be able to move according to a movement of a piston rod to be fitted into the second cylinder, and an annular piston ring having ends in a circumferential direction by being partially cut off. A circumferential groove is formed on an outer circumferential of the second piston. The circumferential groove includes a bottom surface, a one-side end surface, and an opposite-side end surface. The piston ring is axially movably disposed in the circumferential groove. The piston ring includes axial abutment portions, and radial abutment portions at the both ends of the piston ring. When the piston ring abuts against the one-side end surface of the circumferential groove, a first passage is forced between the one-side end surface and an end surface of the piston ring.