A digital piano apparatus includes an input unit including a plurality of keys and a plurality of pedals, a sound source unit, a sound field synthesizing unit, and a speaker unit. The sound field synthesizing unit includes virtual sound source spot signal generating means for generating a plurality of virtual sound source spot signals of a number equivalent to the number of output channels in the speaker unit, the plurality of virtual sound source spot signals being used for forming reproduced sound fields of a grand piano on the basis of a plurality of tone signals supplied from the sound source unit; mixing means for mixing each virtual sound source spot signal with the remaining virtual sound source spot signals; and sound effect means for applying a sound effect by signal processing using impulse responses to the virtual sound source spot signals.