PURPOSE: To improve cutting efficiency and accuracy in parallelism by defining the distance between the shaft and the tip of a peripheral cutting edge and the relation between the inside and outside diameters of a ring type objet, and rotating and cutting said ring type object.

CONSTITUTION: A ring type object 1 to be cut is fixed to a collared shaft and rotated. Using a peripheral cutting edge 4 which satisfies a condition that the relation among the outside diameter D and the inside diameter (d) of the ring type object 1 and the distance l between the shaft surface and the tip of the cutting edge of the peripheral cutting edge 4 is, D/2>l>(D-d)/2, a rotating ring type object 1 is cut by means of cutting feed in the direction of A or B. Due to this construction, the cutting efficiency and accuracy in parallelism can be improved.