A keyless entry system includes an on-vehicle unit and a mobile device, and controls on-vehicle equipment using a wakeup signal and a command signal. The on-vehicle unit radio-transmits a first transmission signal including the wakeup signal and a second transmission signal relating to the detection of an interference wave to the first transmission signal to the mobile device using radio signals having different frequencies. When the first transmission signal has been normally received, the mobile device radio-transmits a third transmission signal including the command signal to the on-vehicle unit and receives a second transmission signal. When the first transmission signal could not be normally received, the mobile device performs the detection of the interference wave to the first transmission signal and radio-transmits a fourth transmission signal for requesting the retransmission of the first transmission signal to the on-vehicle unit.