According to the present invention, provided are an image discrimination apparatus and an image discrimination method for determining whether diaphragmatic radiation has been employed to obtain an autoradiograph of an object using a radiographic device having a diaphragmatic radiation function. According to the image discrimination apparatus and the image discrimination method of the present invention, 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 the autoradiograph has been obtained by using diaphragmatic radiation. Therefore, so that preferable image processing can be performed, it is possible to precisely determine whether diaphragmatic radiation was employed when an autoradiograph of an object was obtained using a radiographic device having a diaphragmatic radiation function, whether a designated portion in an autoradiograph of an object, which is obtained by a radiographic device having a diaphragmatic radiation function, 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 of an object that is obtained by a radiographic device having a diaphragmatic radiation function.