VARIABLE RELIEF VALVE DEVICE

A variable relief valve device includes: a valve body (20) including a first valve portion (22) and a second valve portion (26), the first valve portion having a front end forming a first pressure receiving surface (23), and the second valve portion having a larger diameter than the first valve portion and having a second pressure receiving surface (27) with a larger pressure receiving surface area; a cylinder (30) having an inner peripheral surface formed in two stages to have a step (35) correspondingly to outer diameters of the first valve portion and the second valve portion, including a pressure chamber (38) formed across the step between the first valve portion and the second valve portion, and opening in a fluid passage (4) on a side of the first pressure receiving surface of the valve body; a spring (28) for pressing the valve body toward the fluid passage; a valve hole (42) opening in a portion of the cylinder in which the first valve portion slides, and opened against an pressing force of the spring by the valve body receiving, on the first pressure receiving surface, pressure of a fluid flowing in the fluid passage; a relief passage (40) communicating with the valve hole; and a switching valve (60) for switching between communication between the fluid passage and the pressure chamber and communication between the pressure chamber and the relief passage.