PURPOSE: To quickly respond to change and improve stability by controlling degree of opening of a control valve for nonreformed fuel supplied to a reformer based on an output signal of a fuel cell and a differential pressure signal in front and in rear of a reformed fuel control valve on input side of the cell.

CONSTITUTION: Flow rate of nonreformed fuel G is controlled with a valve 2 and supplied to a reformer 3 and reformed to reformed fuel H. Flow rate of reformed fuel H is controlled with a valve 4 and supplied to a hydrogen electrode 5A of a fuel cell 5. Output of the cell 5 is detected with a current detector 18 of a converter 10, and by its signal, degree of opening of the reformed fuel control valve 4 is controlled through a computing element 19, an adder 20, and a multiplier 22. An advanced control signal obtained by calculating a detected signal with a computing element 30, and a differential signal in front and in rear of the valve 4 detected with a detector 26 are added to an adder 29 to control flow rate of the valve 2. Since nonreformed fuel G is controlled by cell output and also controlled by differential pressure in front and in rear of the valve 4, quick responce to change is obtained and stability is increased.