A method of detecting a spot shape of a pulsed laser beam, includes applying a pulsed laser beam having a wavelength absorbable by an inspection wafer held on a chuck table continuously to the inspection wafer with a focused point on an upper surface of the inspection wafer thereby to form a plurality of laser spots on the upper surface of the inspection wafer. An image of the laser spots is captured, and profiles of shapes of the laser spots are extracted from the captured image of the laser spots. A degree of similarity between the captured image and the profile of an ideal laser spot shape is calculated and stored in a memory. The shapes of the laser spots are found to be improper if the calculated degree of similarity is lower than a threshold value.