1. An X-ray imaging apparatus comprising: a multi X-ray source which includes a plurality of X-ray foci to generate X-rays by irradiating X-ray targets with electron beams; a control unit configured to control a detector so that the detector detects X-rays emitted from the multi X-ray source and reached a detection surface; a change unit configured to change relative positions between said multi X-ray source and said detector; and an acquisition unit configured to acquire X-ray detection signals from X-ray irradiation from said multi X-ray source and, after the relative positions are changed by said change unit, acquire X-ray detection signals by detecting X-ray irradiation from the multi X-ray source, wherein the control unit controls a generating unit so that the generating unit generates an X-ray projection image based on the plurality of X-ray detection signals acquired by said acquisition unit at a plurality of positions.