An X-ray tube includes a radiopaque substrate including a window portion, an X-ray transmission window closing the window portion, an X-ray target provided at the window portion from an inner surface side of the substrate, a highly-evacuated container portion attached to the inner surface of the substrate, a cathode, a first control electrode and a second control electrode provided inside the container portion. A shielding electrode is provided at the inner surface of the substrate so as to surround the window portion. Electrons collide with the X-ray target to generate X-rays. Electrons reflected on the X-ray target between the shielding electrodes are absorbed by the shielding electrodes, so an inner surface of the container portion is not charged. The electron emission from the cathode is not affected by the reflected electrons, so a change in target current is small, and thus X-rays of substantially constant intensity can be radiated.