A shock absorber includes a cylinder, a piston that partitions the cylinder into an expansion-side chamber and a contraction-side chamber, a piston rod connected to the piston, a damping passage that allows the expansion-side chamber to communicate with the contraction-side chamber, a pressure chamber that communicates with the expansion-side chamber and the contraction-side chamber, a free piston that partitions the pressure chamber into an expansion-side pressure chamber and a contraction-side pressure chamber, a spring element configured to position the free piston in a neutral position with respect to the pressure chamber and exert a biasing force for suppressing a displacement of the free piston from the neutral position, and a damping force control unit provided in the damping passage, the damping force control unit being configured to change resistance to a flow of the hydraulic fluid passing therethrough.