PURPOSE: To reject noise, by generating an approximate wave to noise in synchronizing with a switching signal for ignition circuit for an internal combustion engine or chopper circuit for a motor and decreasing the output of a receiver for car at noise input.

CONSTITUTION: A thyristor off-pulse is applied to a thyristor chopper circuit 111 from a thyristor gate control circuit 113. A triangle wave generator 115 generates an approximate wave to noise in synchronizing with the pulse. A part of an output of a high frequency amplifier 126 of a receiver 117 for a car passes through a reception level detecting circuit 118 and enters a variable gain amplfier 122. The amplitude of the noise equivalent wave is increased, since the gain of the amplifier 122 is great at a weak reception electromagnetic wave, to lower the gain of an intermediate frequency amplifier 125 through an output lowering circuit 116. Thus, a waveform where noise is suppressed can be obtained without distortion.