Abstract: A spindle device comprises a spindle housing having rotatably mounted therein a hollow tubular spindle and a rotary motor for rotationally driving the spindle. One end of the spindle projects outwardly of the housing, and the other end of the spindle is disposed within the housing. A lubricating oil system flows oil through the hollow spindle to the work tool and the system includes an oil conduit which extends a predetermined extent into the interior of the hollow spindle at the spindle other end with a small clearance between the conduit and the spindle. A helical recess is formed on the outer periphery of the oil conduit, or the inner periphery of the spindle, or both, in the region where the oil conduit extends into the spindle so that during high speed rotation of the spindle, a helical airflow is created in the region where the lubricating oil enters the spindle to prevent the outflow of oil from the spindle other end.