A radiation generating tube, which includes: a cathode connected to an electron gun structure; an anode including a target and configured to generate radiation; and a tubular side wall disposed between the cathode and the anode to surround the electron gun structure; and an electrical potential defining member disposed at an intermediate portion of the tubular side wall between the anode and the cathode. The electrical potential defining member is electrically connected to an electrical potential defining unit via an electrical resistance member or an inductor, and a potential of the electrical potential defining member is defined to be a higher potential than a potential of the cathode and to be a lower potential than a potential of the anode.