A method for deciding correctly a type of a specific area of an image having inclination includes the steps of generating an edge image based on a target image to be a target of image processing, generating a first histogram indicating the number of edge pixels existing in the lateral direction at each position in the longitudinal direction within a predetermined area and a second histogram indicating the number of the edge pixels existing in the longitudinal direction at each position in the lateral direction with respect to the edge pixels that indicate an edge in the predetermined area of the edge image, determining a variance value of a width of a mountain having an extreme value that exceeds a predetermined threshold value in the histograms, and deciding whether or not the predetermined area is one of a table area and a graph area based on the variance value.