An apparatus and method are provided for determining whether diaphragmatic radiation has been employed to obtain an autoradiograph of an object using a radiographic device having a diaphragmatic radiation function. An autoradiographic signal is entered and a first characteristic value is calculated using an autoradiograph designated by the autoradiographic signal, and then a frequency is calculated for the appearance of a density value for pixels constituting the edge of the autoradiograph that is determined using the first characteristic value and the frequency is employed to determine whether diaphragmatic radiation was used. So that preferable image processing can be performed, it is determined whether diaphragmatic radiation was employed in obtaining the autoradiograph, whether a designated portion in the autoradiograph is an irradiation area, and whether a plain image (an image produced when radioactive rays do not pass through an object but directly irradiate a sensor) is present/absent in the autoradiograph.