A method in which an acoustic sensor disposed in a polishing apparatus can be accurately calibrated is disclosed. In this method, polishing sounds of a substrate are acquired using an acoustic sensor; and then at least two distinctive sounds, having distinctive frequencies respectively, are selected from the acquired polishing sounds. Further, the at least two distinctive sounds are output from a sound source coupled to any of a polishing table, the acoustic sensor, and a substrate holder to cause the at least two distinctive sounds to be input to the acoustic sensor. Next, output values of the acoustic sensor are calibrated, such that the output values of the acoustic sensor relative to the at least two distinctive sounds come within an allowable range.