PURPOSE: To attain listening of a radio broadcast even with deteriorated S/N ratio by forming a parallel circuit of low impedance equivalently to an antenna circuit only when a power semiconductor element is changed over.

CONSTITUTION: An intermediate circuit 14 for preventing noise radio wave is provided between control driver 1 and an antenna terminal 13 of a radio receiver. While width setting circuits 16A, 16B triggered by a command signal switching a power transistor (TR) of a DC chopper device 4 are moved, the impedance of an impedance control circuit 18 is controlled and the impedance is controlled highly again just after the switching of the power TR. Thus, the gain of an antenna circuit of noise radio wave generated by the TR of the DC chopper 4 is decreased remarkably, the radio broadcast is listened to.