A pattern inspection device has a light irradiator configured to irradiate a light on an inspection area set in a pattern forming location on a semiconductor wafer and an adjustment area set different from the inspection area in association with the inspection area on the semiconductor wafer, an image pickup part for inspection configured to pick up a light which is irradiated by the light irradiator and reflected on the inspection area to generate an inspection image, a tester configured to conduct a pattern inspection of the semiconductor wafer based on the inspection image, an image pickup part for adjustment configured to pick up a light which is irradiated by the light irradiator and reflected on the adjustment area to generate an adjustment image, and a light amount adjuster configured to adjust an amount of the light irradiated on the inspection area by the light irradiator so as to reduce a fluctuation of a luminance of the inspection image due to a difference of a thickness of the pattern based on the adjustment image.