an automatic player piano is implemented with an automatic player unit and a mechanical piano having a keyboard mounted on a key bed , and the automatic player unit has a controller operative to memorizing pieces of a key touch information respectively representative of grades of intensity assigned to the sounds in the recording mode of operation and retrieve the pieces of the key touch information in the playback mode of operation , a plurality of actuators provided in association with the keyboard and responsive to the pieces of the key touch information for causing the keys to move , and a sensor unit operative to detect key motions of the keys for producing the pieces of the key touch information in the recording mode of operation , wherein the sensor unit is provided between the keyboard and the key bed because the space therebetween is largely equal regardless of the model of the mechanical piano .