PURPOSE: To achieve the reduction of noise by producing the sounds of the same frequencies as those of the noise generated from a motor from a speaker provided toward the motor.

CONSTITUTION: Silencing signal is outputted at the same frequencies as those of the noise generated by an armature 1 and with a deviation of phase by a time T from a speaker 14. Hence, by adjusting the position of the speaker 14 and the time T, the negating action owing to synthethis of the sounds of opposite phases is accomplished and the noise may be reduced.