A rotary anode X-ray tube apparatus according to an embodiment of the present invention includes a stationary shaft, a cooling bath that is provided in the stationary shaft, a rotary cylinder that is rotatably supported to the stationary shaft, a target that is provided in the rotary cylinder, a cathode that is disposed to face the target, and a vacuum enclosure that stores these components. The stationary shaft has a large-diameter portion provided in a portion thereof and is provided with a flow passage through which a cooling fluid flows. The cooling bath is provided by thinning the wall thickness of the large-diameter portion to increase the flow passage diameter of a portion of the flow passage. The rotary cylinder covers an area of the stationary shaft including the large-diameter portion through a liquid metal and is rotatably supported to the stationary shaft. The target has a hollow circular plate shape that is provided on an outer circumferential surface of the rotary cylinder. The vacuum enclosure stores the stationary shaft, the rotary cylinder, the target, and the cathode and supports the stationary shaft.