A fuel cell system includes a fuel cell, a secondary cell, a voltage transformer, and a control portion. The control portion charges the secondary cell with surplus electric power at the time of starting the fuel cell, and adjusts voltage of the fuel cell between an open-circuit voltage and a high-potential-avoiding voltage in the case where the secondary cell is expected to become overcharged while the output voltage of the fuel cell is decreased from the open-circuit voltage to the high-potential-avoiding voltage. The foregoing case is at least one of the case where a passage electric power that passes through the voltage transformer exceeds a secondary cell-charging-purpose permitted-to-pass electric power, the case where the input electric power restriction value for the secondary cell is exceeded, and the case where amount of regeneration by the mover that is charged is not restricted.