A radiation generating tube includes an electron emitting source configured to emit an electron beam; a target configured to generate radiation when the target is irradiated with the electron beam; a rear shield body having a tube-shaped electron passage with openings thereof at each end of the passage, and being located at the side of the electron emitting source with respect to the target, a first opening of the passage facing the electron emitting source and being separated from the electron emitting source, a second opening of the passage facing the target; and a brazing material joining the rear shield body with a peripheral edge of the target, at a position separated from the second opening. A closed space isolated from the electron passage is provided between the target and the rear shield body.