A phase contrast image is generated on the basis of a plurality of
radiation images of an object taken in imaging positions which are
different from each other in the distance from the object. An
enlargement/reduction processing is carried out on the radiation images
as taken in the imaging positions according to the distances between the
imaging positions so that the radiation images become substantially the
same in their sizes, and a phase contrast image is generated on the basis
of the radiation images thus processed.