A diagnostic imaging system includes a generation unit which generates a fluoroscopic image of X-rays that irradiate a subject, a setting unit which, when displaying the fluoroscopic image superimposed on a field image of a head mounted display, sets the display ratio of the field image and the fluoroscopic image in accordance with a display condition, an image composition unit which generates a composite image by superimposing the fluoroscopic image on the field image on the basis of the ratio set by the setting unit, and an image display unit which displays the composite image on the display unit of the head mounted display.