To improve draining efficiency of water trapped in a fuel cell.

When a fuel cell stack is made to generate electricity by a control unit (a step S1), a cell voltage of the fuel cell stack is monitored by a cell voltage sensor (a step S2), and when the cell voltage is judged to be lower than a predetermined value (a step S3), a hydrogen gas supply regulator is controlled so as to raise fuel gas pressure (a step S4), and then, a purge open/close valve is controlled to switch from a closed state to an open state (a step S5). With this, a kinetic pressure of hydrogen gas pressure is generated to make an anode electrode side drain efficiently. Then, the cell voltage is estimated to be higher than the predetermined value (a step S6), the purge open/close valve 6 is controlled to switch from an open state to a closed state (a step S7).

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