In response to extension and compression of a piston rod, a piston slidingly moves in a cylinder, causing a flow of hydraulic oil. The hydraulic oil flow is controlled by a disk valve to generate a damping force. An elastic seal member fixed to the rear side of the disk valve is fitted to a recess in a pilot body to form a pilot chamber. The valve-opening operation of the disk valve is controlled by the pressure in the pilot chamber. The elastic seal member has an extension extended and fixed to the front side of the disk valve. Thus, forces acting on the rear and front sides of the disk valve due to shrinkage of the elastic seal member during fixing process balance and cancel each other out. Accordingly, it is possible to prevent warping of the disk valve and to obtain stable damping force characteristics.