PURPOSE: To effectively perform protective stopping of a fuel cell power generator over a wide load range by protectively stopping a fuel cell power generator during its operation when the output voltage of a fuel cell goes down beyond a predetermined limit voltage which is determined in response to the d.c. output current value of the fuel cell.

CONSTITUTION: The control of generated power quantity is performed in such processes that chemical reaction amounts of a fuel reformer and a fuel cell 1 are controlled by means of a control signal transmitted t0 an auxiliary machinery control unit 6 after a reactive gas amount is computed by an arithmetic control unit 10 which receives on external load instruction, and at same time the arithmetic control unit 10 computes a current value and voltage value in accordance with an instruction power to control a power inverter 3 through a control unit 9. The purpose of the protective stopping unit of a fuel cell power generator is achieved by monitoring the d.c. output voltage Vd and the d.c. output current Id of the fuel cell 1 by a voltage detector 7 and a current detector 8, respectively, and having such signals outputted, as forcing the arithmetic control unit to reduce the chemical reaction amounts of a fuel processing unit 2 and the fuel cell to zero and the output of the power inverter 3 to zero by means of an instruction signal 11S generated by a protective stopping means 11 which receives detection signals 7S, 8S.