The device includes: a signal generating unit generating a millimeter wave signal by signal processing of an input signal; a coupling circuit transmitting an electromagnetic wave from the millimeter wave signal generated by the signal generating unit to one end of a circuit board; a coupling circuit receiving the electromagnetic wave from the millimeter wave signal from the other end of the circuit board; and a signal generating unit that generates an output signal by signal processing of the millimeter wave signal from the electromagnetic wave received by the coupling circuit. Preferably, the circuit board is constituted by a dielectric material whose the dielectric loss tangent is relatively large, and a transmission line functioning as a millimeter wave transmission path is constituted within this circuit board. With this construction, extremely high-speed signals can be transmitted through a circuit board having a prescribed dielectric constant representing a large loss.