A fuel cell system includes a fuel cell, a motor, a scroll type compressor, connected to the air feeding pipe of the fuel cell and a scroll type regenerator connected to the air exhaust pipe of the fuel cell. The movable scrolls of the compressor and the regenerator are coupled to opposite ends of the motor output shaft in symmetry with each other. A pressure ratio of the regenerator is selected to be smaller than that of the compressor by an amount corresponding to a pressure loss of the exhaust gas across the fuel cell, so that the rotation of the regenerator never transmits a negative torque to the motor output shaft MC. Therefore, the regenerator can efficiently provide power assistance to the compressor.