To provide an audio signal processor capable of reducing the circuit scale of a FIR (Finite Impulse Response) filter for digital-filtering audio signals different in sampling frequency.

A sampling rate converter 1 down-converts an audio signal Xs based on a rate , and supplies it to FIR filters 2a and 2b to make the FIR filters 2a and 2b perform digital filtering. The FIR filter 2a and 2b are formed of FIR filters whose number of taps are determined according to the duration of an impulse reply to be generated in the case of performing the digital filtering of the audio signal whose sampling is performed by a sampling frequency which is equal to a reference frequency fbase within the range of a predetermined frequency band under operating frequencies fa and fb which are equal to the reference frequency fbase.