1. An image processing device comprising: a feature data calculator configured to calculate feature data of each pixel in an image or each area acquired by dividing the image into a plurality of areas; an approximate shape calculator configured to calculate an approximate shape approximating a profile of a distribution area in which the feature data is distributed in a feature space having the feature data as an element; and an abnormal area detector configured to detect an abnormal area in the image based on the approximate shape and the profile of the distribution area, wherein the approximate shape calculator comprises a graphic fitting unit configured to fit a geometric graphic to the profile of the distribution area, and uses a graphic fitted by the graphic fitting unit as the approximate shape.