Abstract: An X-ray tube for analytic use comprises a bottomed cylindrical nozzle which is formed at the bottom with a slit having substantially the same shape and size as that of a focus formed on an electron-impact surface of an anode target. A pair of recesses are formed out in the backside surface of the anode. The nozzle is provided on its outer periphery with a pair of engaging members fitted into the recess, respectively, to prevent the rotation of the nozzle relative to the anode target. Consequently, the nozzle is detachably fitted to the anode and rotated substantially together with the anode thus resulting in a sure alignment of the slit of nozzle with the focus of target.