An X-ray imaging system is provided with an X-ray source (11), first and second absorption gratings (31, 32), and a flat panel detector (FPD) (30), and obtains a phase contrast image of an object H by performing imaging while moving the second absorption grating (32) in x direction relative to the first absorption grating (31). The following mathematical expression is satisfied where p1′ denotes a period of a first pattern image at a position of the second absorption grating (32), and p2′ denotes a substantial grating pitch of the second absorption grating (32), and DX denotes a dimension, in the x-direction, of an X-ray imaging area of each pixel of the FPD (30). Here, “n” denotes a positive integer. DX≠n×(p1′×p2′)/|p1′−p2′|