A rotary-anode X-ray tube having a rotor, a stationary shaft, and a sliding bearing connecting the rotor and the stationary shaft, forming a gap filled with liquid metal lubricant. The rotor has a first rotary member supporting an anode target and a second rotary member at which a sliding bearing is installed and which is coaxial with the first rotary member. The first and the second rotary members are connected at that end of the heat conductive path which is remote from the anode target. A heat insulating gap is formed at all fitting portions, but the remote end. Therefore, the temperature rise of the sliding bearing is controlled without using refregerant, and stable rotation of the bearing is secured.