[Problems to be Solved]When an area in which it is difficult to detect a periodic pattern is further included in a radiation field area, allowing a periodic pattern to be detected accurately.[Means for Solving the Problems]The image obtaining unit (31) obtains a radiation image (P0) from the radiation detector (2), the radiation field area detection unit (32) detects a radiation field area (P1) from the radiation image (P0). The analysis area setting unit (33) detects a direct radiation area, a superabsorbent body area, and a high noise area as the areas where a periodic pattern is unlikely to present and sets an analysis area (P2) by excluding these areas. The frequency analysis unit (34) performs a frequency analysis only on the analysis area (P2) and detects a frequency component of the periodic pattern arising from a grid. The filtering processing unit (35) removes the frequency component of the periodic pattern arising from the grid from the radiation image (P0).
