To provide a flaw inspection device having an optimized cycle for enhancing the classification precision of a flaw, and to provide a flaw inspection method.

The flaw inspection device has a floodlight projection means for projecting light on an inspection target, a light detecting means for detecting the transmitted light or reflected light through the inspection target and a data processing means for inspecting the flaw of the inspection target on the basis of the transmitted light or reflected light detected by the light detecting means. The data processing means is constituted of a flaw place extracting means, a flaw classifying means and an adjusting means and the adjusting means adjusts a threshold value and/or a filter for detecting a flaw place in a flaw place extracting means on the basis of the output of the flaw classifying means.