Abstract: An electric vehicle includes a main battery mounted on a vehicle body and a sub-battery detachably connected to the vehicle body. The electric vehicle travels with the electric power of the main battery in the case where the traveling distance is not long. In the case where the traveling distance is long, a trailer with the sub-battery is coupled to the rear of the electric vehicle, so that both the electric powers of the two batteries are used to drive an electric motor to allow the electric vehicle to travel. At the time of driving of the motor, the electric power of the sub-battery is preferentially used. When the sub-battery becomes completely discharged, the trailer is disconnected from the electric vehicle. In this case, with the vehicle body weight reduced, the traveling of the electric vehicle with the electric power of the main battery can be continued, and therefore the total traveling distance is further increased.