To reduce acoustic noise without newly providing a dedicated speaker to generate a pseudo noise acoustic wave for reducing the acoustic noise from an acoustic noise source.

A pseudo noise signal from an adaptive filter with a signal from a reference microphone 21 for referring to a noise sound of an acoustic noise source 20 as a reference input is supplied to a built-in speaker 54 for sound reproducing, the pseudo noise acoustic wave for reducing the acoustic noise from the acoustic noise source is generated, and a residual component of the acoustic noise from the acoustic noise source is converged by an error microphone 24. Then, a signal from the reference microphone is supplied to a delay means having a prescribed transfer function and delayed just for an acoustic route between the built-in speaker and the error microphone, an output of the delay means is supplied to a least square mean calculating means as a reference input, a least square mean of a residual signal from the error microphone is calculated and according to the operated result, an adaptive filter coefficient of the adaptive filter is determined.