According to one embodiment, a button telephone set, comprising function keys equipped with light emitting devices, respectively, display device which displays character information, failure information receiving unit which receives data notified from the exchange, display determining unit which determines display types of the function keys from types of the received data, light emitting device control unit which display-controls the light emitting devices of the corresponding function keys in response to an instruction from the display determining unit, display device control unit which performs a data display onto the display device in accordance with the instruction from the display determining unit, key operation determining unit which determines depressed states of keys of the button telephone sets including the function keys, and key operation transmission unit which transmits the depressed states of the keys to the exchange.