PURPOSE: To enable a rotating ball and an inner ring both to be directly cooled by inserting a cooling air feeding pipe into a clearance part between both inner and outer rings holding the rotating ball, in an improved rotary bearing for a machine tool or the like.

CONSTITUTION: A cooling air feeding pipe 4 is inserted from an outer ring 1 into a gap with an inner ring 2, and its pipe port 41 is opened to a clearance between the inner ring 1 and the outer ring 1 from the pipe port 41. Then, cooling air is sprayed to a clearance between both these rings 1 and 2. In addition, a lubricating oil feeding pipe 5 is also installed there and opened to a gap with its pipe port 51, thereby feeding these inner and outer rings with lubricating oil. With the blowout of this cooling air, an outer surface of the inner ring 2, an inner surface of the outer ring 1 and a rotating ball 3 all come into contact with the cooling air directly and cooled.