Overflow valve

The relief valve has a piston including a first piston member that presses the biasing member by the pressure of the pilot oil in the pilot chamber and changes the amount of deflection of the biasing member. The first piston member has: a first pressure receiving surface that receives the pressure of the hydraulic oil from the first oil chamber in one direction in the axial direction; and a second pressure receiving surface that receives the pressure of the hydraulic oil from the second oil chamber in the other direction in the axial direction. 溢流阀具有活塞，该活塞包含第1活塞部件，该第1活塞部件借助先导室内的先导油的压力按压施力部件而使施力部件的挠曲量变化。第1活塞部件具有：第1受压面，其承受来自第1油室内的工作油的朝向轴向一方的压力；以及第2受压面，其承受来自第2油室内的工作油的朝向轴向另一方的压力。