Abstract: An X-ray tube apparatus is disclosed, which comprises a vacuum envelope and, an anode target and a cathode assembly both disposed in the envelope and facing each other. The cathode assembly includes a filament for emitting an electron beam, filament supports for supporting the filament and a beam shaping electrode for passing through the electron beam from the filament and focusing the electron beam. The filament has a flat sheet-like electron emission portion, a pair of U-shaped portions provided at the opposite ends of the electron emission portion, in such manner that they extend from the opposite ends in the direction away from the anode target and bend back toward the anode target, and a pair of supported end portions each extending from the U-shaped portions.