An X-ray tube according to an embodiment of the inventive concept includes a cathode structure; an anode structure spaced vertically from the cathode structure, a gate electrode structure disposed between the cathode structure and the anode structure, an emitter array disposed between the cathode structure and the gate electrode structure, a tube sheath configured to connect the cathode structure and the anode structure, and a fixing unit connected with the gate electrode structure. The cathode structure includes a first rotation shaft and a cathode connected with the first rotation shaft as one body. The gate electrode structure includes a second rotation shaft and a gate electrode connected with the second rotation shaft through a bearing, and the second rotation shaft is connected with the first rotation shaft by a coupling unit. The gate electrode includes a gate electrode substrate and a protruding part that protrudes from the gate electrode substrate toward an emitter. The protruding part of the gate electrode includes a gate hole that vertically overlaps the emitter. The fixing unit includes a ferromagnetic structure attached to one surface of the gate electrode substrate and disposed on an outer portion of the substrate and a permanent magnet disposed adjacent to the ferromagnetic structure with the tube sheath therebetween.