A sample which includes a region exhibiting a large density change, such as, bones or lungs and a region exhibiting a small density change, such as, biological soft tissues, and whose measurement is difficult to do for conventional absorption and phase contrast X-ray imaging apparatuses is highly sensitively imaged and observed. In a phase contrast X-ray imaging apparatus using an X-ray interferometer, a reference object whose shape and internal density distribution are analogous to those of a sample and which is known is positioned on an optical path other than an optical path in the interferometer on which the sample is positioned.