A method of determining voltage conditions of a fuel cell vehicle which includes a motor as a driving force source of the vehicle, a motor control device for controlling operation of the motor, a fuel cell, to which a reaction gas is supplied, for generating electric power by an electrochemical reaction, and a battery device which is charged by the electric power generated by the fuel cell and sends and receives electrical energy to and from the motor by control of the motor control device. The method includes setting a voltage value, typically an average value, of an output voltage of the fuel cell within a range from a minimum value to a maximum value of an open circuit voltage of the battery device. Even when the fuel cell and the battery device are directly connected, overcharge or overdischarge can be prevented, thereby reducing frequency of voltage conversion.