PURPOSE: To faithfully reproduce the acoustic characteristic of a natural musical instrument by the circuit constitution of a small scale by providing an acoustic processing means for performing each different acoustic processing to each component of each distributed musical tone signal.

CONSTITUTION: Musical tone signals outputted from sound sources TGk (k = 1 to n) are distributed into three in a prescribed distribution ratio, respective ly, and with respect to each distributed signal, each different filter processing is executed by all pass filters AP1 to AP3 and each circuit succeeding to them, and also, signals obtained as a result of the processing are superposed, and moreover, added directly added to a sound signal, and outputted as a musical tone signal for the left channel and a musical tone signal for the right channel. Accordingly, the musical tone signal of the sound source TG adjusts each multi plication coefficient of multipliers MEk (k =1 to n), MFk (k = 1 to n), and MGk (k = 1 to n) in accordance with each degree belonging to high, middle and low compasses, and can vary the contents of the filter processing performed to each musical tone signal in accordance with a sound pitch. In such a way, the acoustic characteristic being equal to a resonator of a natural musical instrument by the circuit constitution of a small scale.