According to which a damper is operated before or after keying, one of two resonances is generated. A second waveform storage 18 storing original waveform data of a first resonance based on a music sound including an impact sound of keying according to a before-key-pressing pedaling, and a third waveform storage 19 storing original waveform data of a second resonance based on a music sound which does not include an impact sound of keying according to an after-key-pressing pedaling, are provided. A switch 20 is switched according to the state of the pedal at the time of key pressing to supply selected resonance waveform data to a resonance generating unit 16. The resonance signal outputted from the resonance generating unit 16 and a music sound signal of a direct sound of keying are added by an adder 24 and inputted into a sound system.