FUELL CELL SYSTEM

A fuel cell system includes a fuel cell (34), an evaporation portion (32), a reforming portion (33), a desulfurizer (11a6), a recycle gas pipe (39), a drain pipe (40) including a drain water inlet port (40a) and a drain water outlet port (40b), and a water tank (14) connected to the drain water outlet port at a lower side than the drain water inlet port. The water tank is configured in a manner that a water level is adjustable to be equal to or greater than a predetermined water level (Ls). The predetermined water level is obtained in a case where a reformed gas at a predetermined pressure (Ps) related to a maximum pressure is applied to a boundary surface (Sk) between the reformed gas and water for reforming within the drain pipe and the boundary surface is positioned at the same height as a sealing water limit surface (Sh).