PURPOSE: To improve SN ratio of X-ray image of specimen by extracting the X-ray to the outside by splitting the target into two portions and by providing the anode having aperture corresponding to the irradiation angle of X-ray from the effective target.

CONSTITUTION: The anode 8 is heated by irradiating the target 3 with accelerated electron beam 2 emitted from the filament 1 and it is cooled by flowing the cooling water from the inlet port 9 and exhausting it from the drain port 10. The X-ray emitted from the target 3 is detected by the detector 12 and desired number of line sensors are separately disposed by the electrode plate 13. A specimen is placed between the target 3 and the detector 12. The target 3 is splitted into the sector-shaped effective target 3a and ineffective target 3b. The anode 8 is partly provided with an aperture 11 and width of aperture 11 corresponds to an irradiation angle θ of X-ray emitted from the target 3a. The targets 3a and 3b are placed on the different surfaces. Thereby, an SN ratio of specimen image can be improved.