In order to prevent lubricating oil leakage due to bubbles in a thrust dynamic pressure bearing having herringbone grooves, and to stabilize the bearing performance, and enhance the reliability and durability, auxiliary grooves deeper than pump-in type herringbone grooves for generating dynamic pressure are provided. The bearing inner periphery and bearing outer periphery are linked by a pressure gradient descending slowly, and therefore bubbles present in the bearing inner periphery can be guided to the bearing outer periphery through the auxiliary grooves, and discharged outside of the bearing from the air-liquid interface, so that lubricating oil leakage due to bubbles can be prevented.