To make the structure simple and miniaturizable and give a table strong clamping force.

A clamp ring 8 having a clamping surface on its inner circumference or the outer circumference is provided on a base 1. A table 5, including a pressure surface 10 set on a diameter whose outside or inside circumferential surface includes an interference with respect to the inside or outside circumference of the clamp ring 8, is supported by the base 1 in a rotatable manner, and after clamping the table 5 with interference and supplying pressure oil to the pressure surface 10, the table 5 is made to make a dividing rotation by means of the rotational driving gears by bending the clamp ring 8 in the unclamping direction with respect to the table 5.