PURPOSE: To generate stable X-rays without being influenced by the external magnetism by forming a radiating port to radiate the X-rays outside without absorbing the X-rays in a shielding material to surround an electron beam.

CONSTITUTION: A filament 11 and an anode 14 are held in an electrically insulated condition by both left and right parts of a glass tube 15. An electron beam 2 emitted from the filament 11 collides with a target 13 arranged in an opposite position on the tip of the anode 14 with an electric potential difference from the filament 11, and X-rays 1 are generated. A cathode 12 which is put in the same electric potential with the filament 11 and corrects the emitting direction of the electron beam 2 from the filament 11, is arranged in the vicinity containing the periphery of the filament 11. A shielding material 16 to shield the electron beam 2 from the external magnetism 3 is arranged around the target 13 containing a passage of the electron beam 2 emitted from the filament 11, and a radiating port 17 to pass the X-rays 1 is formed in a part of the shielding material 16.