There is provided a fuel cell system having a moisture mixture separating mechanism capable of separating produced water in high purity. While a sheet member closes an outlet port of a drain port and an inlet port of a drain passage by closely adhering to an outlet-side opening end of the drain port and an inlet-side opening end of the drain passage in a state when hydraulic pressure within a Pitot tube is low, it elastically deforms and separates from the opening ends of the drain port and drain passage when the hydraulic pressure within the Pitot tube increases, thus communicating the outlet-side opening end of the drain port with the inlet-side opening end of the drain passage and discharging water in the drain port to the drain passage.