X-RAY TUBE

The present invention prevents the variation of X-ray intensity with time in a parallel-tube type X-ray tube. An X-ray tube (1) has: an X-ray opaque substrate (4) which has a window unit (3); an X-ray transparent window (8) to close the window unit; an X-ray target (9) which is installed on the window unit from the inner surface of the substrate; a container unit (5) which has high-vacuum inside; a cathode (11); a first control electrode (12); and a second control electrode (14) which are installed inside. A shielding electrode (20) is installed on the inner surface to surround the window unit. Electrons collide an X-ray target and generate X-rays. The electrons reflected toward the X-ray target in between the shielding electrodes are absorbed by the shielding electrodes and are not electrically charged on the inner surface of the container unit. Electron emission of the cathode is not affected by the reflected electrons; the variation of the target current is small; and is capable of emitting nearly the same intensity as the X-rays.