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This paper presents the development of an automatic piano which plays by itself from MIDI(Musical Instrument Digital Interface) file. We can find the MIDI format file in music data files or play data files. Piano tone is extracted from the MIDI fileand the sync time is judged and decided from the extracted piano tone so that the sync time can be sent to master CPU. These data are sent to slave CPU and then to the sound board and solenoid driving circuits. We research and develop sound trace software and sound trace board. This is one of the key technologies for a digital piano keyboard. It transmits the extracted data to the key motion control device which makes the piano playing automatically. Due to the large sound data, NAND flash memory is used to handle the data. Because the read/write speed is very important, main memory is required to be designed as a very fast structure. We designed it to fit the length of the PCB pattern address line. Because we expect large electrical current, SMPS(Switching Mode Power Supply) should be designed in low volume and weight with high power efficiency. We add a regulator to the circuit to supply the constant voltage for the circuit to prevent possible damages. Regulators are 5V and 24V.5V regulator is for MCU and 24V regulator is for solenoid. We designed the optimum key-scan circuit for controlling the 88 keyboards and designed the serial control for the reduced number of wires. The self-playing piano has high growth potential in superior educational effectiveness and a variety of usability. This technology is also likely to be applied to a medical device as music therapy.