In order to provide a method of detecting protrusion of an inspection object from a palette improved to be capable of making highly precise detection and reducing a socket breakage ratio, an inspection object is introduced into each of a plurality of pockets provided on the surface of a palette, which in turn is transported. A reflection level of the inspection object stored in each of the plurality of pockets is measured every palette with a reflection type photoelectric sensor. The maximum value and the minimum value of the reflection level are obtained from data of every palette, for calculating a dispersion width defined by the difference between the maximum value and the minimum value. The dispersion width is compared with a previously set determination threshold, for determining whether or not the dispersion width is greater than the determination threshold.