PURPOSE: To control the cell temperature to predetermined level against the load variation by comparing the temperature of fuel cell with a setting level to obtain the flow then comparing said flow with the flow through a cooling flow path and increasing/decreasing the rotation of a circulation pump.

CONSTITUTION: Cooling water 5 in a tank 4 is circulated through a circulation pump 8 and cooling flow paths 6, 7 in a fuel cell 1 to perform cooling. Here, the temperature of cell 1 is detected through a detector 11 and compared with a setting level 10 in a controller 13 to produce a setting flow 14 which is further compared with the cooling water 5 flow detected through a detector 15 in a controller 17 to produce the rotation operating amount 18 of pump 8 thus to increase/decrease the rotation. When varying the temperature in accordance to the variation of the cooling water 5 flow through the cooling flow paths 6, 7, the temperature of the cell 1 can follow after the temperature variation due to the load variation while the response is with quickened response and maintained at predetermined level.