In an X-ray source 1 and an X-ray tube 4, there is formed a shield portion 42 adapted to shield the portion W where a target support body 18 and an opening portion 34 on the other end side of a valve 20 are fixed to each other when viewed from the one end side of the valve 20. Therefore, the generation of discharge between the one end side of the valve 20 and the fixation portion W can be suppressed. Also, the other end portion of the valve 20 is formed as a narrowed portion 37 and the opening portion 34 on the other end side of the valve 20 is fixed to the target support body 18, whereby the shapes of the valve 20 and the shield portion 42 can be made simpler than in conventional X-ray tubes in which an inner cylindrical portion is formed in a valve. Such a simple structure can improve the stability of an electric field in the valve 20 when generating X-rays and thereby achieve an effective suppression of the generation of discharge in the valve 20.