To prevent faulty lubrication by temporarily storing oil air at a passing place and by surely supplying oil of sufficient quantity to a bearing.

A main shaft 7 is supported by a housing 8 via a rolling bearing 10 and the housing 8 has a nozzle 6 to jet oil air 11 for lubrication to the rolling bearing 10. The bearing 10 is constituted by an inner ring 1, a rolling body 2, an outer ring 3 and a rolling body retaining ring 4. The nozzle 6 jets oil air 11 at the contact surface of the outer ring 3 and the rolling body 2 from the end surface side of the bearing 10. Two line of air pockets 5 where oil air 11 is temporarily stored are engraved on the rolling surface of the outer ring 3 where oil air 11 is passed. The air pocket 5 may be formed on the rolling body 2.