In a semiconductor wafer with a supporting tape attached to the back side of the wafer, a coating member having a refractive index close to that of the supporting tape is formed on a pear-skin surface of the supporting tape to thereby planarize the pear-skin surface. Thereafter, a pulsed laser beam is applied from the upper side of the coating member to the semiconductor wafer in the condition where the focal point of the pulsed laser beam is set at a predetermined depth in the semiconductor wafer. Accordingly, the pulsed laser beam can be sufficiently focused inside the semiconductor wafer to thereby well form a modified layer inside the semiconductor wafer.