In a cordless apparatus, a main device and an additional device each has a communication unit that is capable of selecting a radio channel used for radio communication from a plurality of radio channels of which frequencies are different from each other. The main device has a transmittance control unit that transmits radio signals intermittently from the communication unit of the main device during standby of the additional device, and changes the radio channel on every transmittance of the radio signals. The additional device has a signal strength detection unit that detects a signal strength of the radio signal when the radio signal transmitted from the main device is received by the communication unit of the additional device during standby of the main device, and a notification unit that notifies the signal strength of the radio signal detected by the signal strength detection unit.