Abstract: A rotary anode X-ray tube accommodated in a housing together with oil has a journal box fixed and inwardly extending inside the tube, an anode target fixed to a rotor supported by the journal box and a cathode member opposing the anode target and fixed at an end portion inside the tube opposing the journal box. The fixing portion between the rotary anode X-ray tube and the journal box is supported by a resilient support member on the housing and vibration damping means is disposed on the support member. The vibration damping means includes a moving member fixed at its center and a fixed member fixed to the housing so as to encompass the moving member with a predetermined gap, and oil is fully charged in the gap. Vibration of the rotation system is transmitted to the moving member and the operation of this member damps the vibration by means of the squeeze action of the oil.