In a fuel cell system, a temperature sensor detects an internal temperature of
a fuel cell. A cooling water pump is controlled so that it is stopped when the
internal temperature of the fuel cell is equal to or lower than 0 degrees. A driving
amount of the cooling water pump increases according to a rise in internal temperature
of the fuel cell when the internal temperature is higher than 0 degrees. A degree
of increase in driving amount is restrained when the internal temperature of the
fuel cell is between 0 degrees and a predetermined temperature higher than 0 degrees.
