A cylinder body is partitioned by a partition into a first chamber that is divided from an outside by a cap body and a second chamber accommodating a piston body. A flow channel communicating the first chamber and the second chamber with each other is formed in the partition, and a shaft is projected from the partition onto the first chamber side. The cap body includes a through-hole, the shaft is inserted movably in the through-hole from a reference position along an axis line direction of the cylinder body. There is provided a throttle structure that changes a gap between the through-hole and the shaft when the cap body moves from the reference position by a pressure change generated by a movement or a relative movement of the piston body.