A shock absorber including a piston (3) slidably fitted in a cylinder having hydraulic oil sealed therein. A flow of hydraulic oil, induced in a passage (10) and a sub-passage (29) by sliding movement of the piston in the cylinder in response to the stroke of a piston rod, is controlled by an extension main valve (14) and a compression sub-valve (15) incorporated in the extension main valve, thereby generating a damping force. The amount of deflection of a sub-disk (30) constituting the compression sub-valve when the sub-disk is opened is limited by restricting portions (21). The sub-disk is provided with communicating holes (31) to reduce a differential pressure acting on the sub-disk when opened and also to relax the concentration of stress in the sub-disk, thereby improving the durability of the sub-disk.