A control valve is provided with a poppet valve (61) which moves in the axial direction relative to a seat hole (21) and changes the cross-sectional area of the flow passage of the seat hole (21). The control valve is also provided with a spring disc (40) which presses the poppet valve (61) against a return spring (12) in the direction in which the poppet valve (61) opens. The spring disc (40) is provided with: a secondary pressure receiving surface (48) which is a portion moving in association with the movement of the poppet valve (61) and which is subjected to a secondary pressure conducted to a secondary port (77); and a pilot pressure receiving surface (49) which is subjected to a pilot pressure which is a reference pressure. The spring disc (40) elastically deforms according to the pressure difference between the secondary pressure and the pilot pressure and moves the poppet valve (61) in the axial direction.
