An X-ray imaging tube comprising an vacuum envelope, and input screen located in the input end of the envelope, an output screen located in the output end of the envelope, an anode located in the output end of the envelope, and a plurality of beam-converging electrodes located in the envelope and arranged along the inner surface of the envelope. The tube has an magnification of used input field size of 2.3 or more. The components of the tube have such positions and sizes, thus satisfying the following relations:3.5.ltoreq.G3.sub.D /A.sub.D .ltoreq.5.0-3.65.times.MAG+1.00.ltoreq.G3.sub.L /L.ltoreq.-3.65.times.MAG+1.05where L is the distance between the input and output screens, A.sub.D is the inside diameter of the anode or one of the beam-converging electrodes set at the same potential as the anode, which is closer to the input screen than any other beam-converging electrodes set at the same potential as the anode, G3.sub.D is the inside diameter of one of beam-converging electrodes set at potential of at least 2 KV, which is closer to the input screen than any other electrode set at potential of at least 2 KV, G3.sub.L is the distance between the input screen and the electrode set at least 2 KV and located closer to the input screen than any other electrode set at least 2 KV, and MAG is the image-reducing ratio of the X-ray imaging tube.