Abstract: An arbor clamping apparatus providing a steady way for clamping boring arbor and improves structure rigidity and boring accuracy for boring and milling machines. The milling arbor of the present invention is designed and characterized by two steps spindles and includes the first step spindle used mainly to clamp a boring arbor and to hold large cutting tools and fixtures, and the second step spindle designed principally to support and contain the boring arbor. With the first step spindle a clamping mechanism is established and includes a hydraulic cylinder, a piston and movable wedges. Hydraulic force is applied through the action of the piston to drive the wedges to move between the boring and milling arbors and hence the clamping for a boring arbor is achieved through the approaching action of the wedges.