To improve utilization efficiency of energy in a fuel cell.

The fuel cell main body 1 is provided with: a collecting plate 2; a collecting plate 3; and a plurality of membrane electrode junctions 4 as well as a plurality of double-sided separators 5 alternately laminated between the collecting plate 2 and the collecting plate 3. An anode gas flow channel 71 is formed at one face of each double-sided separator 5, and a cathode gas flow channel 76 at the other face, and a heat exchange flow channel 73 is formed inside the double-sided separator 5. When a measurement temperature T of a temperature sensor 60 is below a preset threshold temperature T1, a control part 101 opens a valve 22 at an opening level of Vh, and opens a valve 23 so as to reach a given flow volume at an opening level of Va to prevent overcooling with in-flowing cathode gas. When the measurement temperature T of the temperature sensor 60 is over the preset threshold temperature T1 and below a danger threshold temperature T2, the control part 101 fully opens the valve 22, and opens the valve 23 by an opening level of Vb.