The X-ray imaging device comprises an X-ray source that is able to move along a predetermined movement path, a movement unit configured to cause the X-ray source to move along the predetermined movement path, an imaging platform that is disposed to face the X-ray source, a flat-panel X-ray detector that is provided to the imaging platform, a marker that is disposed in the imaging platform, a control unit that causes the X-ray source to move and to capture images respectively including the marker from at least two positions, and an image processing unit that calculates a position of an image of the marker in each of the captured images and calculates a slope of a movement axis of the X-ray source with respect to the X-ray detector based on a relative relationship between positions of images of the marker.