To reduce a noise when a control signal is processed without a special mute circuit by fade-in processing an output signal when signal processing of audio and video, etc., is interrupted and fade-out processing the output signal when the signal processing of the audio and video, etc., is restarted.

The steps 25, 26 of the fade-in processing, fade-out processing are added into a main routine 21 as the processing when the interruption for the step 23 of audio signal processing A is started, or is ended. That is, when an operation part performs operation of setting revision (e.g. switching of start/ stop of filtering processing, rewriting of a filter coefficient, switching of start/ stop of delay processing, rewriting of delay time, etc.,) at a certain point of time, HOST.I/O interruption occurs, and the processing of the audio signal processing A in the step 23 is interrupted. Thereafter, the fade-in processing is performed. Further, when the execution of an external processing routine 31 is ended, the fade-out processing is performed in the step 26.