To properly control a polishing amount in polishing of a disk-like substrate, and suppress dispersion of quality of the disk-like substrate after being polished.

A doughnut-like glass block 40 is housed in a disk holder 11. A polishing liquid is supplied to at least an inner peripheral end face of the doughnut-like glass block 40. A polishing brush 13 is inserted into the hollow part of the doughnut-like glass block 40, and is rotated around a brush rotary shaft 12 to polish the inner peripheral end face. A control section 20 monitors data of an actual rotation speed for a prescribed time, calculates an average value of the actual rotation speed, and defines it as a representative value of the actual rotation speed. The control section 20 calculates a×[the representative value of the actual rotation speed]+b (a, b: coefficients calculated beforehand for each brush and for each set rotation speed) on the basis of the representative value of the actual rotation speed, and calculates the polishing work time from a start till end of an end face polishing process. In a polishing device 1, the end face polishing process is carried out for the calculated polishing work time.