A method of this invention involves capturing an image of an outer periphery of a semiconductor wafer, by use of a CCD camera, performing image analysis on data about the captured image, detecting defects such as chips and cracks on the outer periphery of the semiconductor wafer, storing positions of the respective defects, calculating a clearance between the adjacent defects from information about the stored positions, comparing the calculated clearances with a preset width of a separation tape, and obtaining the clearance larger than the width of the separation tape, by arithmetic processing. If some of the clearances are larger than the width of the separation tape, this method also involves setting an appropriate one of the clearance as a position where the separation tape is joined, performing alignment on the semiconductor wafer, joining the separation tape to a protective tape joined to a surface of the semiconductor wafer, and separating the protective tape together with the separation tape from the surface of the semiconductor wafer.