1. A radiography apparatus with a function for evaluating image quality, comprising: a radiating-generating unit for emitting radiation; an imaging unit for converting the radiation into image data; a measuring unit for measuring an image-quality evaluating value of the image data; and a determining unit for determining the image quality of the imaging unit based on a plurality of image-quality evaluating values of the image data acquired at a plurality of points in time, each image-quality evaluating value corresponding to the image data acquired at one of the points in time.