An embodiment of the inventive concept provides an X-ray tube including a chamber having a hollow pillar shape using a first axis as a central axis, a cathode electrode disposed on a bottom surface of the chamber, an emitter provided at a position at which the cathode electrode meets the first axis, an anode electrode including a through-hole using the first axis as a central axis and a target layer inclined to the first axis, a gate electrode disposed between the cathode electrode and the anode electrode and having an opening exposing the emitter, a focusing electrode disposed between the gate electrode and the anode electrode, a window spaced apart from the target layer of the anode electrode, and a window electrode provided on a top surface of the chamber to fix a side surface of the window. Here, the window electrode is grounded.