The relay board includes a first end face opposed to and fixed to the first surface of the conductive block, a second end face opposite to the first end face, and a top and a bottom defining thickness of the relay board. The top has a slope at a position closer to the first end face than the second end face. The slope inclines such that the thickness decreases in a direction from the first end face to the second end face. The conductor layers include a signal pattern on the top with part of the signal pattern disposed on the slope, and a first ground pattern extending from the bottom to each of the first end face and the second end face. The signal wire has one end bonded to the signal lead pin and another end bonded to the signal pattern on the slope.