To achieve an image processor that reduces streak artifacts while suppressing a degradation in spatial resolution in a reconstructed image.

The image processor includes: a generating means for generating an image representing a high-frequency component of a reconstructed image P; a detecting means that executes processing for detecting a pixel pattern CP, in which one pixel is a noted pixel AP, and N or more pixels having the same magnitude relation with respect to a prescribed reference value of a pixel value and including the noted pixel AP are continuously arranged side by side in the linear direction D3 in an image generated by the generating means, and that detects the noted pixel AP as the candidate for a pixel showing components st of streak artifacts in a reconstructed image P when the pixel pattern is detected; and a reducing means for reducing streak artifacts in the reconstructed image P on the basis of the candidates detected by the detecting means.