An automatic player piano includes an acoustic piano and an electronic system for reenacting a performance on the acoustic piano; a self-diagnosis subroutine program runs on a microprocessor of the electronic system so as to diagnose solenoid-operated actuators with built-in plunger sensors and component parts of the acoustic piano such as keys, pedals, action units and hammers on the basis of pieces of plunger data, pieces of key data and pieces of hammer data; thus, the mechanical components of the piano are diagnosed as well as the electric components through the execution of the self-diagnosis subroutine program.