Abstract: A cordless telephone apparatus includes a radio transceiver for cordless communication with a slave unit. A controller is operative for controlling the radio transceiver. A main power supply is operative for generating electric power from commercial ac power. An auxiliary battery is operative for generating electric power. The radio transceiver and the controller are activated by either the electric power generated by the main power supply or the electric power generated by the auxiliary battery. A voice amplifier connected between an external telephone line and the radio transceiver is operative for amplifying a speech signal transmitted between the external telephone line and the radio transceiver. The voice amplifier is activated by electric power fed from the external telephone line.