An automatic player piano is a combination between an acoustic piano and an automatic playing system, and a grand piano and an upright piano are used as the acoustic piano; the grand piano has action units prompter than action units of the upright piano so that a half-stroke recorded through the grand piano is not reproducible by the upright piano; the automatic playing system causes the hammers to rotate toward the strings without any escape thereby compensating the poor promptness with the short keystroke of the keys until the rotation of hammers.