Rear glass is provided with a patch-like radiation conductor and a first ground conductor surrounding the patch-like radiation conductor. An electronic circuit unit includes a base plate fixed on the rear glass; a frame body which houses a circuit substrate and is fixed on the base plate; and a cover for covering the frame body. One surface of the circuit substrate defines a component-holding surface which is connected with a second end of a feeder cable connected with the radiation conductor and the first ground conductor. The other surface of the circuit substrate is provided with a second ground conductor to function as a radio-wave reflective surface. The radio-wave reflective surface faces the radiation conductor and the first ground conductor disposed on the rear glass such that the radio-wave reflective surface is separated from the radiation conductor and the first ground conductor by a predetermined distance.