PURPOSE: To detect the working end point in process by detecting vibration generated during polishing by a vibration sensor installed on a polishing part, passing the vibration detecting signal through a filter to extract a specific frequency band, detecting the working end point according to an extracted vibration detecting signal, and outputting a polishing stop signal.

CONSTITUTION: When abrasive cloth 17 surface-polishes a workpiece l, mechanical vibration generated with polishing is detected by a vibration sensor 24, and a vibration detecting signal sV is input through an amplifier 25 to a band- pass filter 26. The band-pass filter 26 extracts a vibration detecting signal sF of a frequency band of 2kHz-4kHz, for example, and inputs the same to a vibration analyzer 27. The vibration analyzer conducts the FFT processing for the signal, and outputs an analysis signal sA showing the power spectrum to a working end point detecting device 28. If the signal sA exceeds a threshold, the working end point detecting device 28 outputs a working stop signal sS to a working control mechanism 21 to stop working.