1. A dynamic radiographing system comprising: a radiographing device which radiographs dynamically a heart part of a subject by plain radiography and generates X-ray images in a plurality of time phases, the radiographing device including an X-ray source for emitting an X-ray and a detector for detecting the X-ray emitted from the X-ray source; an image analysis device for calculating an evaluation value relating to a heart function using the X-ray images in the plurality of time phases; a display device; and a control device which allows the display device to display thereon information on the calculated evaluation value.