Disclosed herein is an X-ray imaging apparatus having an improved structure which is configured for preventing an entrance of foreign materials. The X-ray imaging apparatus includes: an X-ray source configured to generate X-rays, and to irradiate the generated X-rays; an X-ray detector configured to detect the irradiated X-rays; and a first frame and a second frame coupled with each other to form an outer appearance of the X-ray detector. The first frame is tightly coupled with the second frame so that no gap exists between the first frame and the second frame in order to prevent a foreign material from entering the inside of the X-ray detector.