To efficiently generate image data by using correction data. First offset data is obtained in advance for each of a plurality of imaging times, and is stored in a second image storage unit. The imaging time requested by a user is selected from the plurality of imaging times by a control unit, and an object is shot in the selected imaging time so as to store image data in a first image storage unit. A correction processing unit offset-corrects the image data by using first offset data corresponding to the selected imaging time and outputs first image data (preview image). In parallel with an output of the first image data, an imaging operation without irradiation is performed to have second offset data on approximately the same condition as actual imaging obtained by the control unit, and the image data is offset-corrected by using the obtained second offset data so as to output second image data.