An electricity converter (7) for controlling an output of the fuel cell (1), a battery (3) for storing electricity of the fuel cell (1), and a load device (5) that operates by electricity of at least one of the fuel cell (1) or the battery (3) are included. Further provided is a controller (25) that calculates current chargeable electricity of the battery (3), load device electricity currently consumed by the load device (5) and current generable electricity of the fuel cell (1), and decreases the output of the fuel cell (1) by the electricity converter (7) when the generable electricity is equal-to or more-than a combined value of the chargeable electricity and the load device electricity.