TELEPHONE SET

PURPOSE:To discriminate the feeding stage depending on a ring back tone by sending a low frequency natural ring back tone at application of commercial power supply and sending a high frequency ring back tone such as a ceramic ringer at power failure. CONSTITUTION:If an incoming call is detected at the incoming call detection standby stage, a power failure detection circuit 12 starts detection of power failure and when the power failure is detected, a switch 9 is thrown to the position of the ceramic ringer 10 and an input/output control circuit 3 uses a ring back tone circuit 8 to generate a 1kHz or 1.2kHz frequency signal to drive the ringer 10. On the other hand, if no power failure is detected, the switch 9 is thrown to the position of a speaker 11, the control circuit 3 uses the circuit 8 to generate a 450 or 600kHz frequency signal to drive the speaker 11.