Patent ID: 8205729

Claim:
A shock absorber, comprising: a cylinder chamber formed in a tube and filled with a liquid; a piston disposed in the cylinder chamber so as to be freely displaced in a direction along an axis line of the cylinder chamber; a piston rod, one end of the piston rod being connected to the piston and the other end of the piston rod extending out from the tube; and an accumulator allowing the piston rod to generate a damping force by receiving the liquid from a compression side of the cylinder chamber when the piston rod is pushed into the tube by an impact force and the piston is displaced, wherein a helical damping groove, inclined relative to the axis line, is formed on an internal periphery of the cylinder chamber so as to directly come into contact with the piston within a stroke range of the piston, and the damping groove includes only one pitch, a groove width of the damping groove is constant over the entire length of the damping groove, a depth of the damping groove gradually decreases along a spiral toward the direction in which the piston rod is pushed in, the groove width of the damping groove along the axis line is equal to or greater than a length of the piston in a direction along the axis line, and a length of the piston in a direction along the axis line is smaller than a pitch of the damping groove.