A shock absorber includes: a cylinder accommodating a fluid; a piston that reciprocates with respect to the cylinder while partitioning an inside of the cylinder into a first fluid chamber and a second fluid chamber; a pump having a first port that communicates with either one of the first fluid chamber and the second fluid chamber and a second port that communicates with the other one of the first fluid chamber and the second fluid chamber, and including a flow rate change portion that changes a circulation amount of the fluid circulating between the first port and the second port; an electric rotor rotating in conjunction with the pump; and a stator forming a magnetic field between the electric rotor and the stator.