When a CPU 11 controls a drawing control and storage unit 14 according to an operation performed on an operation unit 3 not to perform any navigation display on a monitoring unit 2, the CPU controls a switch SW1 to an off state during a time period during which the CPU does not perform this navigation display, and stops the supply of electric power to a secondary storage unit 13 to stop the operation of this secondary storage unit 13, thereby reducing the consumption of the secondary storage unit.