(EN) ABSTRACT OF THE DISCLOSURE ABSTRACT POLISHING METHOD, COMPUTER-READABLE STORAGE MEDIUM STORING PROGRAM FOR OPERATING COMPUTER, AND POLISHING APPARATUS A polishing method includes: during polishing of the workpiece, creating a reference spectrum history and a monitoring spectrum history by repeatedly producing a reference spectrum and a monitoring spectrum at two points on the workpiece; calculating a plurality of reference history differences that are differences between a latest monitoring spectrum and a plurality of reference spectra in the reference spectrum history; calculating a plurality of monitoring history differences that are differences between a latest reference spectrum and a plurality of monitoring spectra in the monitoring spectrum history; calculating a film-thickness difference between a monitoring point and a reference point based on a local minimum point of a reference history difference or a monitoring history difference. FIG. 6