A shock absorber comprising: a cylinder in which oil is filled; a piston slidably fit in the cylinder; a piston rod that is coupled to the piston and extended to an outside of the cylinder; and a damping-force generating device that controls a flow of the 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 is seated on the valve seat, wherein the valve seat includes a valve seat section on which the valve body seats, the channel includes a first channel provided on an upstream side in the flowing direction of the oil with reference to the valve seat section and a second channel provided on a downstream side in the flowing direction of the oil with reference to the valve seat section, the shock absorber further comprises a valve-body backpressure chamber that communicates with the second channel and the plunger chamber and causes oil pressure to act on the valve body in the valve closing direction, a first pressure receiving section, which is at least a part of the valve body, receives oil pressure of the first channel in a valve opening direction, a second pressure receiving section, which is at least a part of the valve body that is different from the first pressure receiving section receives oil pressure of the valve-body backpressure chamber, which communicates with the second channel, in the valve closing direction, wherein the valve body includes a seating section seating on the valve seat section, and a diameter of the seating section is smaller than a maximum diameter of the first pressure receiving section characterized in that a pressure receiving area of the first pressure receiving section and a pressure receiving area of the second pressure receiving section are same. a cylinder in which oil is filled; a piston slidably fit in the cylinder; a piston rod that is coupled to the piston and extended to an outside of the cylinder; and a damping-force generating device that controls a flow of the 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 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 is seated on the valve seat, wherein the valve seat includes a valve seat section on which the valve body seats, the channel includes a first channel provided on an upstream side in the flowing direction of the oil with reference to the valve seat section and a second channel provided on a downstream side in the flowing direction of the oil with reference to the valve seat section, the shock absorber further comprises a valve-body backpressure chamber that communicates with the second channel and the plunger chamber and causes oil pressure to act on the valve body in the valve closing direction, a first pressure receiving section, which is at least a part of the valve body, receives oil pressure of the first channel in a valve opening direction, a second pressure receiving section, which is at least a part of the valve body that is different from the first pressure receiving section receives oil pressure of the valve-body backpressure chamber, which communicates with the second channel, in the valve closing direction, wherein the valve body includes a seating section seating on the valve seat section, and a diameter of the seating section is smaller than a maximum diameter of the first pressure receiving section characterized in that a pressure receiving area of the first pressure receiving section and a pressure receiving area of the second pressure receiving section are same.