A radiation generating apparatus has a radiation generating tube held in a holding container 12 and a cooling medium between the holding container and the radiation generating tube. The radiation generating tube includes an envelope with an aperture, an electron emitting source arranged in the envelope, a target arranged facing the source, for generating radiation responsive to irradiation with an electron beam emitted from the source, and a tubular shield for holding the target by an inner wall thereof and shielding part of the radiation emitted from the target. The shield is arranged to protrude outward of the envelope so that the target is positioned on an outer side of the aperture, and the cooling medium contacts at least a part of the shield.