A shock absorber includes: a cylinder; a piston; a piston rod; and a damping-force generating device that controls a flow of oil, caused by sliding of the piston in the cylinder, wherein the damping-force generating device includes: a valve body that generates a damping force according to opening and closing of the valve body on a channel in which the oil flows; a valve seat on which the valve body seats to close the channel; and an actuator that includes a plunger generating thrust to the valve body in a valve closing direction and a plunger chamber in which the oil is filled in order to actuate the plunger, and the plunger chamber communicates with a downstream side in a flowing direction of the oil with reference to a place where the valve body seats on the valve seat.