An X-ray imaging apparatus for imaging a subject comprising: an X-ray source; a phase grating adapted to transmit X-rays from the X-ray source for forming an interference intensity distribution by the Talbot effect; an absorption grating adapted to partly shield the interference intensity distribution formed by the phase grating for generating a Moire; and a detector adapted to detect information of an intensity distribution of the Moire generated by the absorption grating; an arithmetic unit adapted to calculate information of a differential phase image of the subject from information of the one intensity distribution of the Moire detected by the detector, wherein the phase grating includes phase advance portions and phase lag portions, wherein the phase advance portions and the phase lag portions are two-dimensionally arrayed, wherein the absorption grating includes transmissive portions and shielding portions, wherein the transmissive portions and the shielding portions are two-dimensionally arrayed, wherein the Moire has periods in two directions, characterized in that the arithmetic unit is adapted to obtain information of differential phase images of the subject in two directions from information of the one intensity distribution of the Moire by: (a) performing Fourier transform for the information of the intensity distribution of the Moire to acquire a spatial frequency spectrum, (b) separating a spectrum corresponding to a carrier frequency from the acquired spatial frequency spectrum, and (c) performing inverse Fourier transform for the separated spectrum, and acquiring information of the differential phase images in two directions. an X-ray source; a phase grating adapted to transmit X-rays from the X-ray source for forming an interference intensity distribution by the Talbot effect; an absorption grating adapted to partly shield the interference intensity distribution formed by the phase grating for generating a Moire; and a detector adapted to detect information of an intensity distribution of the Moire generated by the absorption grating; an arithmetic unit adapted to calculate information of a differential phase image of the subject from information of the one intensity distribution of the Moire detected by the detector, wherein the phase grating includes phase advance portions and phase lag portions, wherein the phase advance portions and the phase lag portions are two-dimensionally arrayed, wherein the absorption grating includes transmissive portions and shielding portions, wherein the transmissive portions and the shielding portions are two-dimensionally arrayed, wherein the Moire has periods in two directions, characterized in that the arithmetic unit is adapted to obtain information of differential phase images of the subject in two directions from information of the one intensity distribution of the Moire by: (a) performing Fourier transform for the information of the intensity distribution of the Moire to acquire a spatial frequency spectrum, (b) separating a spectrum corresponding to a carrier frequency from the acquired spatial frequency spectrum, and (c) performing inverse Fourier transform for the separated spectrum, and acquiring information of the differential phase images in two directions. (a) performing Fourier transform for the information of the intensity distribution of the Moire to acquire a spatial frequency spectrum, (b) separating a spectrum corresponding to a carrier frequency from the acquired spatial frequency spectrum, and (c) performing inverse Fourier transform for the separated spectrum, and acquiring information of the differential phase images in two directions.