A layout for an exhaust pipe which also serves as a drainage pipe which prevents splashing of water generated in a fuel cell toward a passenger or splashing toward a tire. Humid excessive gas supplied from a fuel cell is diluted in a dilution box by off-gas discharged from the fuel cell and is used for humidifying air in the humidifier. An exhaust pipe is connected to the dilution box, and diluted hydrogen gas is discharged via the exhaust pipe. Vapor mixed in hydrogen gas is condensed in the exhaust pipe and turned into water, which is drained through the exhaust pipe that extends rearwardly of a vehicle body through the interior of a power unit. A discharge port of the exhaust pipe (which is also a drainage port for water generated in the fuel cell) is positioned at the widthwise center of the vehicle body.