Provided is a foreign matter inspection method for positively detecting a foreign matter in the neighborhood of the edge of a mirror-finished substrate without fail. Edge-emphasis and binarization are performed following the taking of an image of a substrate-under-inspection at a contour of its inspection area, to further detect a plurality of sampling points representative of a contour of the inspection area. An estimated inspection area is determined by determining the size, position and rotation angle of contour lines defined, size-reducibly, from the coordinates of the plurality of sampling points. After applying a mask to the binary image data in an area other than the estimated inspection area, a foreign-matter detection step is performed.