A diaphragm is clamped between a solenoid unit disposed in a casing and a second valve body in which hydrogen is introduced. A filter comprising a bottomed cylindrical mesh member is mounted in a first passage defined in the first valve body. A restriction having an orifice for restricting the flow rate of hydrogen supplied to first and second communication chambers is mounted in a first port that is disposed upstream of the filter. The restriction and the filter are disposed coaxially in line with each other.