There is provided a fuel cell system which can prevent the drying of a proton exchange membrane and prevent the generation of liquid droplets at a hydrogen tank surface which blocks the supply of air, at the same time, and which includes a hydrogen tank, a fuel cell stack disposed such that a first air hole thereof faces the hydrogen tank and a second air hole thereof is open to the atmosphere, and a water holding member provided on a surface of the hydrogen tank facing the first air hole of the fuel cell stack, for collecting and holding water generated in the fuel cell stack.