The hydraulic cylinder having a portion on a side of a lip tip end of an annular clearance between an inner circumferential face of a shaft hole of a cylinder and a piston is made up of a minute clearance in order to suppress protrusion of the lip, wherein an annular clearance area for suppressing occurrence of the cavitation and for shortening an axial distance of the annular clearance portion made up of the minute clearance is formed on an opposite side of the annular clearance portion from a mounting groove.