A cylinder apparatus is configured to compatibly achieve an increase in mechanical strength and a reduction in weight of a metal ring of an oil seal member used in the cylinder apparatus. A hydraulic shock absorber (1) as a cylinder apparatus has a rod guide (9) provided at one end (2A) thereof. An annular oil seal member (10) is provided closer to the one end (2A) than the rod guide (9) so as to face the rod guide (9). The oil seal member (10) is secured by staked portions (2C) of the outer tube (2) between the staked portions (2C) and the rod guide (9). The oil seal member (10) includes a metal ring (11) and a seal member (13). The metal ring (11) is provided with a plurality of radially extending ribs (12) by locally deforming the metal ring (11).