An electronic keyboard musical instrument includes a storage device, a musical tone generation unit, a resonating sound generation unit, and an adding unit. The musical tone generation unit reads out corresponding musical tone waveform data from the storage device according to key depression information to generate a musical tone waveform signal and a first register resonating sound waveform signal. The resonating sound generation unit receives the musical tone waveform signal to cause the resonating sound generation circuit to generate a second register resonating sound waveform signal according to damper pedal operator manipulation information and the key depression information, and outputs the second register resonating sound waveform signal. The adding unit is configured to add the musical tone waveform signal and the resonating sound waveform signal from the musical tone generation unit and the resonating sound generation unit respectively, and outputting a resulting signal.