A system for warning against forgetting to pull out an information recording medium can improve working efficiency upon mounting a navigation unit and an on-board radio unit onto a vehicle, and notify a user of an alarm that causes no uncomfortable feeling, and is still inexpensive to manufacture. A drive unit switch detects when a control part is turned off, also detects, through a communication line, a residual state of an IC card with respect to an on-board device, and notifies the result of the detection to a the voice generation part. When the IC card is "absent" in the on-board device, the control part interrupts the supply of power to the on-board device through the on-board device power supply line.