A method and apparatus for accurately detecting the anomalous shadows occurring within an interimage image based on two or more images obtained of the same subject, wherein the artifacts occurring in the interimage image are reduced, is provided. A temporal subtraction image formed by an interimage processing means is subjected to a morphology process wherein the artifacts occurring in the interimage image are suppressed relative to the actual difference between the two images on which the temporal subtraction image is based. A detecting means detects the suspected anomalous shadows occurring within the temporal subtraction image that has been subjected to an artifact-suppressing morphology process.