To provide an electric power mixing device possessing output control of a fuel cell.

The electric power mixing device possessing the output control of the fuel cell includes a first power supply circuit, and a second power supply circuit. The first power supply circuit includes a first power unit, a first voltage conversion unit, a sensor unit, and a control unit. The voltage conversion unit is connected to the power unit, and includes a step-up circuit of a DC power or a step-down circuit of the DC power. Through this circuit, the DC power of the power unit is converted to the DC power having a specific voltage and the converted DC power is output. The sensor unit detects a voltage or a current of the DC power output by the first power unit, and based on an electric signal fed-back by the sensor unit, the control unit protects the first power unit by controlling conversion proportion of the DC power of the first voltage conversion unit, or by stopping conversion of the DC power of the first voltage conversion unit.