Patent ID: 8646269

Claim:
A cylinder apparatus comprising: a cylinder body including a seal groove provided in a cylinder bore, a cup seal fitted into the seal groove, and a piston slidably inserted into the cylinder bore, wherein the cup seal includes a base portion having a base end surface opposing an opening-side-surface of the seal groove, an inner circumferential lip portion having an inner circumferential surface slidably abutting against an outer circumferential surface of the piston, an outer circumferential lip portion having an outer circumferential surface abutting against a bottom surface of the seal groove, an abutment portion provided on the base end surface of the base portion of the cup seal, and a contact pressure adjustment portion provided on the base end surface of the base portion, and the contact pressure adjustment portion does not contact with an inner circumferential side of the opening-side-surface of the seal groove in a state where the cylinder apparatus is in a non-operational state, and contacts with the inner circumferential side of the opening-side-surface in a state where the cylinder apparatus is in an operational state.