A read out operation for reading out image data from a conversion circuit irradiated with a radiation, and a read out operation for reading out offset image data from the conversion circuit without irradiated with a radiation are selectively conducted, a control is conducted to repeat at a plurality of times the operation for reading out the offset image data, offset data corresponding to each pixel is extracted from one of the plurality of the offset image data to generate corrective offset image data such that offset data corresponding to all the pixels in a row of the matrix is not extracted from one of the plurality of offset image data, and the corrective offset image data is subtracted from the image data to perform an offset correction to render line noise less noticeable, for an offset correction without line noise by a simple signal processing to be provided.
