The invention improves an insulating performance of an X-ray tube without increasing an insulation size. An X-ray tube in accordance with the invention keeps a mechanical strength of a glass insulation material and improves an insulation withstand voltage by a concavity and convexity, by forming a concavity and convexity having an arithmetic mean surface roughness of JIS B0601-1994 equal to or more than 1.0 μm and equal to or less than 10 μm in a vacuum side surface of a glass insulation material supporting electric conductors within a vacuum chamber for a range equal to or more than 2 mm from a position in an end of the electric conductors.