To provide a defect detection method and device of a transparent plate, constituted of a reflection optical system which stably detects a rear surface reflection detected image, highly accurately obtaining the position of a defect in a plate thickness direction and the size of the defect, obtaining a pickup image brighter than that of a conventional reflection optical system and dealing with the case where it is needed that the relative positions of a light source and a camera are accurately disposed such as a case where the boundary of brightness and darkness is picked up.

The camera 3 and the light source 2 are disposed opposite to each other in directions oblique to the front surface of a glass substrate 1 for a liquid crystal panel of an inspection target. A surface mirror 4 is disposed at a prescribed distance from the rear surface of the glass substrate 1 for the liquid crystal panel and the surface mirror 4 is disposed in such a position that the camera 3 can pickup the light source 2 or the part in the vicinity thereof by using reflection of the mirror through the substrate 1 for the liquid crystal panel.