PURPOSE: To provide a noise reducing device which can completely remove prescribed harmonic noise outputted from a power controller adopting a pulse width modulation system.

CONSTITUTION: A current sensor 10 which detects a load current ig is installed to a current path to a load L which is supplied with electric power by means of a PWM signal Se from a PWM signal generator PS. A frequency analyzing section 20 measures the frequency spectrum of the load current ig detected by means of the sensor 10 and a signal processing section 30, inverse Fourier transformation section 40, and PLL section 50 generate a noise canceler signal Sd for removing prescribed harmonic noise and superimpose the signal Sd upon the PWM signal Se from the generator PS. As a result, the influence of the harmonic noise on the reception performance, etc., of a radio receiver can be prevented, because harmonic noise components are completely removed from the PWM signal Se.