A fuel cell system comprising: a drive motor serving as a power source for driving a load and driven by electric power; a fuel cell for generating electricity with electrochemical reaction of an oxidation gas containing oxygen to a fuel gas containing hydrogen and supplying the electric power to said drive motor; a first boost device for boosting a voltage output from said fuel cell and enabling the post-boosting voltage to be supplied to said drive motor; a secondary battery capable of charging and discharging an electric power and supplying the electric power to said drive motor with the discharge; a second boost device for boosting a voltage output from said secondary battery and enabling the post-boosting voltage to be supplied to said drive motor; and boost control means for controlling the voltage boost by said first boost device, characterized in that said boost control means is configured to calculate a requested output electric power of said fuel cell in driving said drive motor by adding the motor necessary electric power necessary for driving said drive motor, the electric power in the charge and the discharge of said secondary battery, the electric power loss of said first boost device in boosting the output voltage of said fuel cell if the first boost device performs boosting, and the electric power loss of said second boost device in boosting the output voltage of said secondary battery if the second boost device performs boosting, and to calculate the requested output voltage of said fuel cell from the calculated requested output electric power of said fuel cell, and said boost control means is configured to, when the calculated requested output voltage of said fuel cell is higher than the motor necessary voltage of said drive motor, inhibit the output voltage of said fuel cell from being boosted by stopping said first boost device such that the output voltage of said fuel cell is directly supplied to said drive motor, and thereby perform intermittent operation control of said first boost device. a drive motor serving as a power source for driving a load and driven by electric power; a fuel cell for generating electricity with electrochemical reaction of an oxidation gas containing oxygen to a fuel gas containing hydrogen and supplying the electric power to said drive motor; a first boost device for boosting a voltage output from said fuel cell and enabling the post-boosting voltage to be supplied to said drive motor; a secondary battery capable of charging and discharging an electric power and supplying the electric power to said drive motor with the discharge; a second boost device for boosting a voltage output from said secondary battery and enabling the post-boosting voltage to be supplied to said drive motor; and boost control means for controlling the voltage boost by said first boost device, characterized in that said boost control means is configured to calculate a requested output electric power of said fuel cell in driving said drive motor by adding the motor necessary electric power necessary for driving said drive motor, the electric power in the charge and the discharge of said secondary battery, the electric power loss of said first boost device in boosting the output voltage of said fuel cell if the first boost device performs boosting, and the electric power loss of said second boost device in boosting the output voltage of said secondary battery if the second boost device performs boosting, and to calculate the requested output voltage of said fuel cell from the calculated requested output electric power of said fuel cell, and said boost control means is configured to, when the calculated requested output voltage of said fuel cell is higher than the motor necessary voltage of said drive motor, inhibit the output voltage of said fuel cell from being boosted by stopping said first boost device such that the output voltage of said fuel cell is directly supplied to said drive motor, and thereby perform intermittent operation control of said first boost device.