Abstract: In a remote control system, each time a transmission code is transmitted, a rolling code having a prescribed bit configuration is cumulatively varied. An operation process is performed between each bit data item of the rolling code and each corresponding bit data item of the ID code, whereby each bit data item of the ID code is varied in correspondence with the rolling code, thus setting a variable ID code. Since the ID code itself which is contained in the signal is also varied in correspondence with the variable code, the fixed portion contained in the signal is decreased with the result that the ID code is almost infinitely widely varied. Accordingly, it becomes almost impossible to decode the ID code even if it is intercepted.