Abstract: A telephone set includes an audio system circuit and a data system circuit connected to a data terminal equipment having a data communication function in and an oral communication function. The telephone set includes a power supply circuit connected to a switching system through a telephone line and a current limiting portion for controlling connection between the data system circuit and the power supply circuit. When connection between the telephone set and the switching system is established through the line, power supply to the telephone set from the switching system through the line. The power is only supplied to the telephone set only via the line and the supplied power is further provided separately to the audio system circuit and the data system circuit through the power supply circuit. After the line connection is established, if a short-circuit occurs in the data terminal equipment, the current limiting portion cuts off a power supply path from the power supply circuit to the data system circuit.