According to this invention, mechanical noise from a noise source of a pre-identified device can be removed, while tracing a change in gain of acoustic wave data, and noise is removed by tracing a change over time of the noise source. To this end, the gain of a signal from a microphone is automatically adjusted by an Auto level control unit (ALC). A threshold according to the gain of the ALC is stored in a register. A comparator compares audio data from the ALC with the threshold, generates weighting coefficients k and 1−k based on the comparison result, and outputs them to weighting coefficient multipliers. The weighting coefficient multipliers and an adder calculate a weighted average value of data in a memory that stores weighting coefficients of old frames and the input acoustic wave data, and update the contents of the memory by the calculation result. With this update processing, the memory stores only a NOISE component. A level adjusting unit adjusts data read out from the memory according to the current gain of the ALC. An adder subtracts the adjusted data from the input acoustic wave data, and outputs data after noise removal.