PURPOSE: To attain the time-variation control of a reverberation, to expand application and to improve control efficiency.

CONSTITUTION: A reverberation providing network part 10 is provided with a delay line for delaying an input signal and outputting a delayed signal and an arithmetic circuit for applying prescribed arithmetic processing to an output signal from the delay line in its closed type network and constituted so as to provide a reverberation effect by inputting a sound signal into the network and circulating the signal through the delay line. Change control data to be optionally set up and controlled by an operator are generated, and an optional parameter out of reverberation setting parameters such as a signal delay time and a loss coefficient in the network part 10 is selected and modulated by the change control data. Consequently, the reverberation setting parameter can be modulated and controlled at real time and reverberation characteristics can simply be changed and controlled.