PURPOSE: To stabilize the secondary side pressure and obtain a small-sized device by installing a cutoff valve, first and second control valves in a main passage, lowering the primary side pressure in two stages and controlling the second control valve by the secondary side pressure and the intermediate pressure.

CONSTITUTION: In an ordinary state, a cut-off valve 4, the first and second control valve 5 and 6 are opened, and the gas supplied from an inlet 2a obtains a prescribed intermediate side pressure, passing through a port 4a and a port 5a. Further, a diaphragm 5c is moved vertically according to the primary side pressure by the control valve 5, and the intermediate side pressure is made constant. Then, the gas is controlled to a prescribed pressure through the passing through a port 6a. Since, at this time, the diaphragm 10b of a servoregulator 10 lowers, the intermediate side pressure is transmitted to a working pressure chamber 10h, and the diaphragm 6c is controlled i n the vertical direction, and the secondary side pressure is made constant. When the secondary side pressure increases abnormally, the cut-off valve 4 is closed, and safety is secured, and whole of the device can be made small-sized.