A dose measured from region information, X-ray information, and a captured image in a previous imaging operation and a dose of radiation obtained from a DAP meter are saved as pieces of information. A dose used in a first imaging operation is based on the saved pieces of information, and a dose to be used in a second imaging operation is estimated from region information or X-ray information in the second imaging operation. If there is a significant difference between the dose in the first imaging operation and the estimated dose for the second imaging operation, a warning is issued. If an image of a region is captured for testing purposes, a warning is not issued.