Impedance mismatching points such as a VIA and a connector on a differential line between a differential driver element and a differential receiver element are arranged in predetermined positions. That is, the impedance mismatching points are arranged in such positions that a transmission time of a digital signal transmitted through a main differential line becomes (integral multiple of UI) ±0.5×Trf, whereby noises are generated within the rise and fall times of a signal to be able to maintain an excellent waveform of the signal.