With a view to providing a bearing mechanism exhibiting a high leakage preventing effect for a liquid medium and an X-ray tube having such a bearing mechanism, the bearing mechanism includes a gap between a plain bearing and a shaft, with a liquid medium being present in the gap, the gap comprising at least three concentric annular gaps communicating in series with one another. The shaft has a pumping groove formed in an outer periphery surface thereof at a position facing the gap. The liquid medium is a liquid metal. The liquid metal is gallium or an alloy thereof.