A sound generator is actuated by a trigger signal produced from a ringing signal on a telephone line, and a telephone line switching mechanism responds to the trigger signal from the trigger signal generator to disconnect the telephone set from the telephone line during an on state of the ringing signal and connect the telephone set to the telephone line during an off state of the ringing signal. Thus, the sound generator can be used to indicate the reception of a telephone call without actuating the telephone bell, and telephone communication is thereafter possible by hooking-off the telephone receiver. The line switching mechanism is preferably of a type which causes a telephone bell to ring upon a power source failure of the sound generator by connecting the telephone line to the telephone receiver.