To prevent the generation of a rusting phenomenon of a suspension spring, and a damage or an abrasion phenomenon in the seals at the rising and setting end of a cylinder body resulting from that the upper end of a hydraulic shock absorber having a cover to cover from the outer peripheral side of the suspension spring, and a side cover such as a boot, receives a dirt or a muddy water.

This top cover structure is composed by inserting its lower end side in a cylinder body to be an axle side member to compose a hydraulic shock absorber 1 allowable to rise and set, and providing a top cover 6 connecting to the upper end side of a rod body 1a to be a body side member to compose the hydraulic shock absorber 1 in the same way under the liquidtight structure, and providing an air vent hole 6a to the top cover 6, and furnishing an air pipe 6b communicating to the air vent hole 6a, and with an adequate length.