A testing system is incorporated in an automatic player piano for specifying a half pedal point of a damper pedal at which the loudness of tones is lessened, and an automatic player moves the damper pedal to the half pedal point so as to lessen the loudness of tones in an automatic playing; the testing system accumulates pieces of experimental data expressing relation between the loudness of tones and a current pedal position of the damper pedal, and searches the pieces of experimental data for points of reflection; and the testing system determines the half pedal point through an internal division on the line between the points of reflection.