The cameras (10) of this X-ray detector are all mounted on a common rigid plate (1) by a surface support and screwed to ensure their optical distance from a scintillator (7) itself mounted on the plate (1) by an enclosure (6) forming a darkroom (8). The common mounting of the principal elements of the detector on a single rigid plate thus significantly reduces image deterioration produced by deformations of the detector, of thermal or mechanical origin.