Detection accuracy of X-ray dosages, to be applied to control the amount of irradiated X-rays, is improved in a mammography apparatus that employs solid state detectors as X-ray image detecting means, and that is capable of interchangeably utilizing solid state detectors of various sizes, without adversely influencing detection of images by the solid state detector. A solid state detector, for recording image information by receiving irradiation of X-rays that bear the image information, and for outputting image signals that represent the recorded image information, an X-ray dosage detector, for detecting the amount of irradiated X-rays, and a moving grid, for removing scattered radiation, are housed within a detecting unit, stacked in this order. The detecting unit is configured to be removably attachable to an imaging table of a mammography apparatus. Thereby, interchangeable use of detecting units having solid state detectors of various sizes housed therein is enabled.