When a compartment internal transmitter of a vehicle-side unit transmits a request signal with vehicle doors opened, at least one of strength of the request signal and sensitivity of a hand-held device to receive the request signal are set at a level lower than a normal level. Thus, even when the vehicle doors are in an open state, a communication area of the compartment internal transmitter is prevented from being extended to cover the outside of the compartment. As a result, when the holder of the hand-held device operates any of the vehicle doors from a location outside the vehicle compartment, it is possible to avoid an erroneous assumption that the hand-held device is left behind in the vehicle compartment and to execute a sequence of consecutive operations.