When an operator presses an exposure switch in step S104, X-ray imaging is executed. Radiation field recognition is performed in step S105. In step S106, density adjustment is performed by obtaining characteristic features of an image in the radiation field. The density-adjusted image is displayed on a display unit in step S107. If the operator gives a crop instruction in step S108, the flow advances to step S109 to check the image size of the designated and extracted region. At the same time, characteristic features are extracted from the image. That is, in the embodiments, it is checked whether an image in an extracted region has characteristic features attached an imaging method button for "finger". If it is determined in step S110 that the extracted region is valid, the flow advances to step S115. If it is determined that the region is invalid, the flow advances to step S111 to execute notification processing.