1. An image inspection method wherein an object to-be-inspected is illuminated by transmission illumination means, and illumination light transmitted through the object to-be-inspected is imaged as a transmission image by imaging means, so as to inspect the object to-be-inspected, comprising: a first step of imaging the transmission image; a second step of applying a quadratic differential filter to the transmission image, thereby to convert the transmission image into a quadratic differential filter image; a third step of binarizing the quadratic differential filter image with a predetermined threshold value, thereby to convert the quadratic differential filter image into a first binarized image; a fourth step of binarizing the transmission image with another predetermined threshold value, thereby to convert the transmission image into a second binarized image; a fifth step of performing a binary feature quantity measurement for the first binarized image and the second binarized image, thereby to calculate binary feature quantities; and a sixth step of deciding a quality of the object to-be-inspected from the binary feature quantities.