A valve is disposed in a reactant gas system apparatus of a fuel cell system. The valve includes a housing having an internal channel as a passage of water, and heaters in the form of rods inserted into the housing. An orifice having a small channel cross sectional area is provided at a predetermined position of the channel. The heaters are inclined from a solenoid of the valve in an axial direction of the housing, and front ends of the heaters are positioned close to the orifice.