Shock absorber

A shock absorber comprising:

• 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 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;
• a stator forming a magnetic field between the electric rotor and the stator;
• a first valve connected to the first fluid chamber and the second fluid chamber and having a high pressure port and a low pressure port, in which one of the first fluid chamber and the second fluid chamber having a higher fluid pressure than the other one of the first fluid chamber and the second fluid chamber is switched to communicate with the high pressure port and the other one of the first fluid chamber and the second fluid chamber is switched to communicate with the low pressure port by a valve body provided in the first valve, wherein
• the pump has a fluid rotor holding a plurality of vanes, and a ring member with which the vanes come into contact,
• the flow rate change portion has a first pressure chamber that applies the fluid pressure of the low pressure port to the ring member so as to increase the circulation amount, and a second pressure chamber that applies the fluid pressure of the high pressure port to the ring member so as to reduce the circulation amount, by flow paths different from flow paths by which the first and second fluid chambers communicate with the first and second ports, and
• the ring member is reciprocatable in a direction perpendicular to a rotation axis of the fluid rotor by a biasing portion that biases the ring member along a direction of application of the fluid pressure by the first pressure chamber.