To discriminate the type of a radiation image from a number of image types previously defined by the region of radiography, the direction of radiography, and the method of radiography, etc.

The discrimination means is for determine to which type, among a plurality of types previously defined by at least one of the region of radiography, the direction of radiography or the method of radiography, the image to be discriminated belongs based on the quantity of characteristics of the plurality of types in the image to be discriminated. The discrimination means, created from mechanical learning using a plurality of sample images belonging to the types prepared for each kind, is prepared. The boundary between the irradiation field and the mask for restricting the irradiation field on the radiation image is detected, and the density is corrected to approximate the image density in the regions on both sides of the boundary in the radiation image. The discrimination means is applied to the density-corrected image, so that the type of the image to which the radiation image belongs is determined.