PURPOSE: To reduce the calculation volume to increase the processing speed while displaying a sufficient noise reduction effect.

CONSTITUTION: A reference signal (x) consisting of an impulse train which has the same period as noise like indistinct sound is read in, and a period of time (k) elapsed till the present time after generation of the latest value of the reference signal is counted with a sampling clock SCp as the unit by a reference pulse counter 11. Each time the time (k) is counted, a count Wmi of a series Wm is supplied to each loud speaker as a driving signal ym (y1 to y4). Meanwhile, a count Wmi of the series Wm in the place determined by the time (k) and delay information d1m read out correspondingly to a period N of the noise is updated by an adaptive processing part 14 based on a residual noise signal e1 (e1 to e8) so that the noise in a vehicle is reduced.