An X-ray apparatus includes a rotation-anode type X-ray tube which is configured such that a rotatable anode target and a cathode that is disposed to be opposed to the anode target are accommodated within a vacuum envelope, a stator which generates an induction electromagnetic field for rotating the anode target, a housing which accommodates and holds at least the rotation-anode type X-ray tube, a circulation path which is provided near at least a part of the rotation-anode type X-ray tube, and through which a water-based coolant is circulated, and a cooling unit including a circulation pump, which is provided at a position along the circulation path and forcibly feeds the water-based coolant, and a radiator which radiates heat of the water-based coolant, wherein an amount of dissolved oxygen at 25.degree. C. in the water-based coolant is 5 mg/liter or less.