An automatic player piano is only equipped with key sensors, and the automatic player is expected to give rise to hammer motion to be varied together with the loudness of tones; the manufacturer prepared not only a velocity conversion table expressing a relation between measured values of the hammer velocity and measured values of the reference key velocity but also a reference table expressing a relation between measured values of hammer velocity and target values of reference key velocity through experiments, and the velocity conversion table and reference table were stored in a suitable memory in the automatic player; the automatic player determines a playback table partially through an experiment and partially through transcription from reference table so as to drive the hammers without influence of unstable key motion at large loudness.