A communication channel establishing method is provided that is used in a communication system including a base station that transmits a beacon on a predetermined communication channel and a communication apparatus that receives the beacon from the base station and establishes communication with the base station using the predetermined communication channel. The method involves detecting at the base station whether a main power supply has been shut off, driving the base station by a backup power supply and transmitting a power supply shutoff notification signal from the base station to the communication apparatus upon detecting that the main power supply has been shut off, storing a current communication channel of the communication apparatus when the power supply shutoff notification signal from the base station is received by the communication unit, and reestablishing communication with the base station at the communication apparatus using the stored current communication channel upon recovery of the main power supply.