Patent ID: 8156856

Claim:
A hydraulic cylinder, comprising: a cylinder having a shaft hole; a piston inserted into the shaft hole so as to have clearance with respect to an inner circumferential surface of the shaft hole; and seal members arranged in annular grooves formed in an inner circumference of the shaft hole to seal an annular gap between the inner circumference of the shaft hole and the piston, wherein in the hydraulic cylinder in which cavitation could occur in a portion of the clearance accompanying motion of the piston, an expansion part obtained by expanding a portion of a sidewall surface of the annular grooves on an inner circumferential edge side outward from an arrangement area of the seal members is provided to make a distance from a location where cavitation occurs to the seal members longer by a space formed by the expansion part, wherein the expansion part is immediately adjacent to and extending directly from the annular grooves.