JPH0828226B

PURPOSE:To prevent any deterioration of the material of the electrode by preventing the open circuit voltage for checking the distribution of reaction gas from exceeding a given level. CONSTITUTION:When the temperature of a stack 1 reaches about 120-130 deg.C, current feeding to the heater is shut off and the stack 1 is then heated by battery reaction. Prior to heating the stack 1 by the heat of battery reaction, the open circuit voltage is measured to check the distribution condition of the reaction gas. Specifically, a fuel supply bulb 7 is opened and valves 8 and 9 for introducing an inactive gas such as nitrogen are opened to and nitrogen gas to the fuel gas and air supplied to the stack 1 thereby reducing hydrogen partial pressure in the fuel gas and oxygen partial pressure in the air. The thus produced reductions in hydrogen and oxygen partial pressures cause a decrease in the characteristic of each electrode thereby resulting in suppression of the open circuit voltage. Accordingly, it is possible to prevent any deterioration of the material of the electrode.