A semiconductor mask correcting device is provided with an image acquiring unit acquiring a mask image, an extraction unit extracting only a main pattern from the mask data, an inspection unit inspecting a defective portion by comparing the extracted main pattern with a main pattern which is obtained from the mask image after a drawing by matching to each other, and a correction unit correcting the defective portion specified by the inspection unit, wherein the extraction unit includes a recognition section recognizing the main pattern and the assist pattern as a figure, a specification section specifying the assist pattern from figures which is recognized on the basis of a predetermined condition, and a main pattern extracting section extracting as the main pattern a figure other than the assist pattern.