A remote control system for a car-mounted device capable of realizing communication performance required for a keyless function and communication performance required for a smart function while suppressing increase in circuit scale. The remote control system includes a portable unit and an in-car unit. The portable unit includes: a function judgment mechanism judging whether the keyless function or the smart function is used; an amplification mechanism controlling transmission power in response to a result of judgment obtained at the function judgment mechanism; and a system clock generator controlling a transmission band in response to a result of judgment obtained at the function judgment part. The in-car unit includes: an in-car function judgment mechanism judging whether the keyless function or the smart function is used; and in-car system clock generator controlling a receiving band in response to a result of judgment obtained at the in-car function judgment mechanism.