To always obtain a natural reverberation effect without adversely affecting the attenuation characteristic of the reverberating sound added at the time of controlling the intonation of the sound by an expression(EXP) pedal.

A multiplaying means 4 being the volume control means to control the volume of musical sound signals based on the operating amount data of an EXP pedal 7 is provided on the front stage of a reverberation device 2. The volume control by the pedal 7 is conducted against the original sound from a musical sound generating circuit 10 and no control is conducted against reverberation sounds. Thus, even though the pedal 7 is operated while a reverberation effect is added, the attenuation characteristic of the reverberation sound is not adversely affected by the volume change of the pedal 7.