A digital image detector and a digital image detecting method using gratings are provided. The digital image detector includes a fluorescent screen that receives X-rays passing through an object, converts the received X-rays into rays and outputs the converted rays, a first reflecting plane that reduces an image based on the rays output from the fluorescent screen in a first axis direction using a grating, a second reflecting plane that reduces the image reduced by the first reflecting plane in a second axis direction using a grating, and an imaging device that receives the image reflected and output from the second reflecting plane, focuses the received image, and converts the focused image into an electrical signal.
