The present invention relates to an X-ray image processing device and an X-ray image processing method using a small X-ray detector, in which the device includes a controller configured to control an X-ray source and an X-ray detector to obtain m (m is an integer of 2 or more) number of consecutive divided projection images at each of preset n (n is an integer of 1 or more) number of imaging angles while rotating around a rotary axis and facing each other, a projection image synthesizing unit configured to generate a synthetic projection image by synthesizing the m number of divided projection images obtained in correspondence to each imaging angle, and an image reconstructor configured to generate a reconstructed image by reconstructing the synthetic projection image.