1. An X-ray imaging apparatus comprising: an X-ray interferometer constituted by a splitting device for splitting an incident X-ray beam into a first X-ray beam and a second X-ray beam, a reflecting device for reflecting a first split X-ray beam and a second split X-ray beam, and a combining device for combining a first reflected X-ray beam and a second reflected X-ray beam; means for placing a sample in an optical path of an arbitrary beam of said first and second x-ray beams; means for placing a phase shifter in an optical path of an arbitrary beam of said first and second x-ray beams; a detector for detecting an interference X-ray beam emitted from said X-ray interferometer; and a processing portion for obtaining an image representing a change in an amplitude of the interference X-ray beam caused by said sample from an output of said detector.