PURPOSE: To make the use by an operator easy, by equipping a dial switch and the like on a steering wheel, in a telephone set on a car.

CONSTITUTION: A steering operation board is provided with a key switch (dial key switch, hook key switch) 90 and a modulation circuit 100, and a fixed side on a car is provided with a telephone section. The fixed device on the car and the steering operation board device are coupled directly by means of slip rings 45, 46 and brushes contacting them, and contactless connection consisting of an electromagnetic coil electrically. The code corresponding to the operation of the key switch is modulated at the modulation circuit 100 from the steering operation board, given to a demodulation circuit 160 at the fixed side on the car and applied to the telephone section through the demodulation at the demodulation circuit 160.