1. An X-ray imaging apparatus comprising: a multi X-ray source which includes a plurality of X-ray focuses to generate X-rays by irradiating X-ray targets with electron beams; a detector which detects X-rays which have been emitted from said multi X-ray source and have reached a detection surface; a moving unit configured to move said multi X-ray source within a plane facing the detection surface; an acquisition unit configured to acquire an X-ray detection signal from said detector for each irradiation by performing X-ray irradiation a plurality of number of times using said multi X-ray source while shifting said multi X-ray source relative to the detection surface by using said moving unit; and a generating unit configured to generate an X-ray projection image based on a plurality of X-ray detection signals acquired by said acquisition unit.