A reading unit reads a first side of a printed material having first image data printed on the first side and second image data printed on a second side, the second side being a back side of the first side, in order to obtain image data. A density determination unit determines whether a density of the second image data exceeds a predetermined density. A comparison unit compares a density of the image data obtained by the reading unit and a density of the first image data, and produces a comparison result. A determination unit, in a case when a density difference between the density of the image data and the density of the first image data exceeds a threshold as the comparison result of the comparison unit, determines that the printed material includes a defect portion.