PURPOSE: To efficiently initialize a memory by routing an input signal.

CONSTITUTION: The digital data outputted from an A/D converter 10 are stored in the memory 12, and the data read out from the memory 12 are converted to an analog signal by a D/A converter 14. Then, by making the read data from the memory 12 the data written before a prescribed time, a prescribed delay signal is obtained. Then, when a delay time is revised by switching a mode, the input signal is muted by a switch 50, and the signal in a soundless state is written in the memory 12, and the memory 12 is initialized. Thus, the memory 12 is initialized surely with simple constitution.