In a radiation imaging system performing a difference process using a stored mask image based on a radiation image obtained before a contrast agent is injected and a radiation image obtained after the contrast agent is injected, a controller displays a first graphic representing a first timing when irradiation of a radial ray is started, a second graphic representing a second timing when the mask image is stored, and a third graphic representing a third timing when the contrast agent is injected in this order along a time axis and controls the second and third timings by the second and third graphics. The controller moves, when one of the second and third graphics is moved along the time axis, the other of the second and third graphics such that an interval between the first and third graphics becomes larger than an interval between the first and second graphics.
