To suppress the excessive consumption of a battery while operating a communication device as far as possible in an electric automobile which is driven with only a battery.

The battery 11 is provided with a residual quantity detection means 23 which detects the residual quantity, and a control circuit 16 gives power to the communication device 20 via a charger 14 and a battery 15 for control from the above battery 11 when a switch 12 for start of vehicle driving, and detects the residual quantity of the above battery 11 by the above residual quantity detection means 23 and stops the power supply to the above communication device 20 when this residual quantity is below a specified value.