The method comprises a first step (S1 in FIG. 1) of obtaining a transmission image, a second step (S2) of applying a quadratic differential filter to the transmission image, thereby to emphasize a part of large luminance change as a quadratic differential filter image, a third step (S3) of binarizing the quadratic differential filter image with a predetermined threshold value, and then storing the resulting binarized image, a fourth step (S4) of binarizing the transmission image with another predetermined threshold value, and then storing the resulting binarized image, a fifth step (S5) of performing the measurement of binary feature quantities for the binarized image stored at the third step (S3) and the binarized image stored at the fourth step (S4), and a sixth step (S6) of deciding the quality of the object to-be-inspected from the binary feature quantities.