PURPOSE: To facilitate adjusting of the irradiating position of electron beam at a target by arranging an electron beam take-out electrode which is asymmetrical against an electron projecting axis in the vicinity of the front face of cathode of an electron gun and applying a variable voltage.

CONSTITUTION: A X-ray generating apparatus will take out an electron beam 2 emitted from a cathode 1 by means of a take-out electrode 11 to irradiate onto a target 4, producing X-ray 5. Here, the take-out electrode 11 is formed asymmetrically against the electron projecting axis to divide the voltage of a high voltage power source 7 through a voltage divider 8, applying a variable positive voltage. The trajectory of the electron beam 2 is determined by an equi-potential distribution 9 to irradiate onto the target 4 while the voltage to be applied onto the take-out electrode 11 is made variable, varying the equi- potential distribution 9. Consequently, the irradiating position against the target 4 can be adjusted easily while the electrical field strength in front of the cathode is increased to increase the output of X-ray.