X-ray tube with a control grid

A grid-equipped X-ray tube including a cathode having a cathode body one end of which is hermetically sealed to one end of an air-sealed envelope and on the other end of which a focusing electrode means is mounted, an anode one end of which is hermetically sealed to the other end of the envelope and on the other end of which a target facing the focusing electrode means is mounted, and a control grid disposed between the cathode and the anode, the improvement in which said focusing electrode means comprises a first focusing electrode having a stepped through bore, a filament insulatingly mounted on the first focusing electrode and part of which extends out through the bore, a second focusing electrode mounted on the first focusing electrode through an insulator and having an opening toward which the filament extends, the second focusing electrode having a potential level the same with that of the filament electrode, and said control grid disposed between the first focusing electrode and the second focusing electrode to cover the filament and each end of which is electrically connected to the first focusing electrode.