To provide a signal input and output device which can input high-frequency signals into an electric wire through which a large current having a low frequency, such as the commercial frequency, etc., is made to flow at a stable level and can output high-frequency signals from the electric wire on a stable level.

This high-frequency signal input and output device 100 is provided with an annular ferromagnetic core 102 arranged around the outer peripheral surface of an electric wire 101, a winding 103 wound around the outer peripheral surface of the core 102 for outputting high-frequency signal for outputting flowing through the wire 101 or inputting the high-frequency signals into the wire 101 and constituted to make a current having a high frequency to flow through the winding 103, and a winding 104 for canceling magnetic field which is wound around the outer peripheral surface of the core 102 and is constituted to make the current having a low frequency, such as the commercial frequency, etc., to flow through the winding 104.