PURPOSE: To high accurately further surely machine an annular work, by applying large pressing force to the work without causing the application of force to the work in the radial direction.

CONSTITUTION: A pressing member 18 is attached by a point contact to a supporting shaft 14 in the axial core through a spherical bearing member 22 and a plane bearing member 23. In consequence, a work W is smoothly moved in the radial direction by centripetal force of the work W, and a rotary axial line 8 of the member 18 is perfectly aligned to a main spindle axial line 2 further large pressing force is applied to the work W without causing the application of force in the radial direction to the work W, and the annular work W is surely rotatively driven without causing the deformation.