An X-ray generator is provided using a transmission type target having a long life span, where it is possible to change the point for generating X-rays on the surface of the target while maintaining the vacuum chamber in a high vacuum state. A portion of a vacuum chamber 1 that includes a target 2 is linked to a main body portion 1a of the chamber through a linking member 5 as a movable chamber portion 1b. A fixed anode 12 is provided between the target 2 and the electrode 10 at the final stage from among a group of electrodes 8, 9 and 10 for electrostatically accelerating and converging electrons from an electron source 7 and is fixed to the main body portion 1a of the chamber in order to prevent the form of the electrical field from changing when the movable chamber portion 1b is shifted.