A rotation table mounted on a machining table of a machine tool includes a clamping mechanism which is driven by air so as to clamp a rotation shaft, and an air purging pressure is applied into a casing so as to prevent a cutting fluid or foreign matter from intruding into the casing of the rotation table. Then, air discharged from the clamping mechanism does not pass through the casing, to which the air purging pressure is applied, and is discharged to the outside of the rotation table through a flow passage.