Offset correction based on offset correction data is performed on radiographic image data that have been read out from a radiation image detector, and the offset correction data are updated. In the offset correction method, correction data for low-frequency components and correction data for high-frequency components, as the offset correction data, are generated based on offset image data that have been read out from the radiation image detector while the radiation image detector is not irradiated with radiation. Further, the correction data for low-frequency components and the correction data for high-frequency components are separately updated.
