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, an output voltage of said fuel cell being set so as to exceed a motor necessary voltage necessary for driving said drive motor in a predetermined speed range of 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; boost control means for controlling the voltage boost by said first boost device on the basis of a correlation between an output voltage of said fuel cell and a motor necessary voltage necessary for driving said drive motor when driving said drive motor; a secondary battery capable of charging and discharging electric power and supplying the electric power to said drive motor by discharging; a buck-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 an inverter supplied with power from the fuel cell and the secondary battery, for converting it to supply the drive motor, characterized in that said boost control means is configured, when a drive state of said drive motor belongs to the predetermined speed range, to restrict the output voltage of said fuel cell from being boosted by said first boost device such that the output voltage of said fuel cell is directly supplied to said inverter, wherein, if a temporary boost ratio, which is a quotient between the motor necessary voltage and the output voltage of said fuel cell, is less than 1 and the output voltage of said fuel cell is between an open circuit voltage of said secondary battery and a maximum output voltage of said fuel cell, or the output voltage of said fuel cell is equal to or smaller than the open circuit voltage of said secondary battery and an output voltage of said first boost device is equal to or smaller than a voltage taking the same value as the open circuit voltage of said secondary battery, the first boost device is stopped, and the output voltage of said fuel cell is applied directly to the inverter. 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, an output voltage of said fuel cell being set so as to exceed a motor necessary voltage necessary for driving said drive motor in a predetermined speed range of 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; boost control means for controlling the voltage boost by said first boost device on the basis of a correlation between an output voltage of said fuel cell and a motor necessary voltage necessary for driving said drive motor when driving said drive motor; a secondary battery capable of charging and discharging electric power and supplying the electric power to said drive motor by discharging; a buck-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 an inverter supplied with power from the fuel cell and the secondary battery, for converting it to supply the drive motor, characterized in that said boost control means is configured, when a drive state of said drive motor belongs to the predetermined speed range, to restrict the output voltage of said fuel cell from being boosted by said first boost device such that the output voltage of said fuel cell is directly supplied to said inverter, wherein, if a temporary boost ratio, which is a quotient between the motor necessary voltage and the output voltage of said fuel cell, is less than 1 and the output voltage of said fuel cell is between an open circuit voltage of said secondary battery and a maximum output voltage of said fuel cell, or the output voltage of said fuel cell is equal to or smaller than the open circuit voltage of said secondary battery and an output voltage of said first boost device is equal to or smaller than a voltage taking the same value as the open circuit voltage of said secondary battery, the first boost device is stopped, and the output voltage of said fuel cell is applied directly to the inverter.