An automatic performance system includes a sign detector configured to detect a sign action of a performer performing a musical piece, a performance analyzer configured to sequentially estimates a performance position in the musical piece by analyzing an acoustic signal representing performed sound in parallel with the performance, and a performance controller configured to control an automatic performance device to carry out an automatic performance of the musical piece so that the automatic performance is synchronized with the sign action detected by the sign detector and a progress of the performance position estimated by the performance analyzer.