This invention relates to a microfocus X-ray tube having a heat-dissipation solid formed on the target adhesively. Specifically, the heat-dissipation solid defining an opening is formed on the target surface irradiated with an electron beam. Heat generated adjacent the target surface by impingement of an electron beam having passed through the opening is promptly distributed by heat conduction through the surface solid. The heat-dissipation solid contributes to lowering of a surface temperature of the target layer with which the electron beam collides, and a reduction of evaporation of a material forming the target, thereby extending an X-ray generating time.