1. An X-ray imaging apparatus comprising: an X-ray generator configured to emit X-rays to a subject in a plurality of times; an X-ray detection panel comprising: light receiving elements, each light receiving element configured to receive X-rays that have passed through the subject, convert the X-rays into electric signals, and output the electric signals corresponding to the X-rays emitted in a plurality of times; and capacitor modules, each respective capacitor module being connected to a respective light receiving element, each capacitor module comprising capacitors connected to a corresponding light receiving element of the light receiving elements and configured to store the electric signals output from the corresponding light receiving element in each capacitor of the capacitors sequentially; and an image processor configured to read out the electric signals stored in each capacitor of each capacitor module of the capacitor modules sequentially after emission of the X-rays in a plurality of times is completed, and to generate X-ray images, wherein the X-ray generator emits X-rays having successively increasing energy levels comprising first X-rays having a low energy level that acquire a basic X-ray image of soft tissues, second X-rays having a medium energy level that separate normal tissues and abnormal tissues in response to the first X-rays, and third X-rays having a high energy level that acquire bones excluding soft tissues in response to the second X-rays.