A variable relief valve device comprising: a valve body including a first valve portion and a second valve portion coaxially formed and axially spaced apart from each other with a shaft therebetween, the first valve portion having a front end forming a first pressure receiving surface, and the second valve portion having a larger diameter than the first valve portion and having a second pressure receiving surface with a larger pressure receiving surface area on a side of the first valve portion; a cylinder in which the valve body axially slides, the cylinder having an inner peripheral surface formed in two stages to have a step to provide inner diameters corresponding to outer diameters of the first valve portion and the second valve portion in sliding ranges thereof, including a pressure chamber formed across the step between the first valve portion and the second valve portion, and opening in a fluid passage through a flow-in passage on a side of the first pressure receiving surface of the valve body; a spring provided in the cylinder to press the valve body toward the fluid passage; a valve hole provided in a portion of the cylinder in which the first valve portion slides, and opened by the valve body receiving, on the first pressure receiving surface, pressure of a fluid flowing in the fluid passage and sliding in the cylinder against a pressing force of the spring; a relief passage communicating with the valve hole; a first communication path (50, 52) having one end opening in the pressure chamber and the other end opening in the fluid passage; a second communication path branching off from the first communication path and opening in the relief passage; and a switching valve provided in a branch portion between the first communication path and the second communication path and capable of switching between communication between the fluid passage and the pressure chamber and communication between the pressure chamber and the relief passage, characterized in that the shaft of the valve body has a smaller diameter than the first valve portion, and the pressure chamber and the flow-in passage both extend axially to make the fluid flow axially. a valve body including a first valve portion and a second valve portion coaxially formed and axially spaced apart from each other with a shaft therebetween, the first valve portion having a front end forming a first pressure receiving surface, and the second valve portion having a larger diameter than the first valve portion and having a second pressure receiving surface with a larger pressure receiving surface area on a side of the first valve portion; a cylinder in which the valve body axially slides, the cylinder having an inner peripheral surface formed in two stages to have a step to provide inner diameters corresponding to outer diameters of the first valve portion and the second valve portion in sliding ranges thereof, including a pressure chamber formed across the step between the first valve portion and the second valve portion, and opening in a fluid passage through a flow-in passage on a side of the first pressure receiving surface of the valve body; a spring provided in the cylinder to press the valve body toward the fluid passage; a valve hole provided in a portion of the cylinder in which the first valve portion slides, and opened by the valve body receiving, on the first pressure receiving surface, pressure of a fluid flowing in the fluid passage and sliding in the cylinder against a pressing force of the spring; a relief passage communicating with the valve hole; a first communication path (50, 52) having one end opening in the pressure chamber and the other end opening in the fluid passage; a second communication path branching off from the first communication path and opening in the relief passage; and a switching valve provided in a branch portion between the first communication path and the second communication path and capable of switching between communication between the fluid passage and the pressure chamber and communication between the pressure chamber and the relief passage, characterized in that the shaft of the valve body has a smaller diameter than the first valve portion, and the pressure chamber and the flow-in passage both extend axially to make the fluid flow axially. the shaft of the valve body has a smaller diameter than the first valve portion, and the pressure chamber and the flow-in passage both extend axially to make the fluid flow axially.