NOVELTY - The fuel cell system (1) has fuel cell containing electrolyte layer, oxidation gas chamber and fuel chamber, ventilation unit, cooling unit, cooling control unit, gas-temperature detection unit, electric current detection unit and flow-rate detection unit. Ventilation unit feeds oxidation gas into inlet of fuel cell. Control unit adjusts cooling capacity of cooling unit based on temperature of oxidation gas fed into inlet, output current value of fuel cell, and air flow of ventilation unit.    USE - Fuel cell system mounted in electric vehicle.    ADVANTAGE - The fuel cell system has improved energy efficiency, and effectively recovers moisture content.    DETAILED DESCRIPTION - The fuel cell system (1) has fuel cell comprising an electrolyte layer for adjoining an oxidation gas chamber and a fuel chamber, a ventilation unit, a cooling unit, a cooling control unit, a gas-temperature detection unit, an electric current detection unit and a flow-rate detection unit. The oxidation gas chamber has an inlet to which oxidation gas flows in, and an outlet in which oxidation gas after reaction is discharged out. Fuel gas is passed into fuel chamber, and reacted with oxidation gas. The ventilation unit feeds oxidation gas into inlet of fuel cell. The cooling unit cools oxidation gas discharged from outlet of fuel cell, and recovers water. The temperature detection unit measures temperature of oxidation gas fed into inlet. The current detection unit detects output current value of fuel cell. The flow rate detection unit detects air flow of ventilation unit. The control unit adjusts cooling capacity of cooling unit based on temperature of oxidation gas fed into inlet, output current value of fuel cell, and air flow of ventilation unit.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of fuel cell system. (Drawing includes non-English language text)    Fuel cell system (1)    Condenser (51)    Fuel cell stack (100)    Air introduction path (123)    Water tank (531)