First and second conductor layers are formed on a main surface of a base layer. A tapered slot is formed between the first and second conductive layers. A first slit is formed at the first conductor layer, and a second slit is formed at the second conductor layer. Thus, the first conductor layer is divided into a first device connection portion and a first antenna portion, and the second conductor layer is divided into a second device connection portion and a second antenna portion. A semiconductor device is connected to the first and second device connection portions.