Abstract: An automatic tool changing apparatus incorporated in a drilling machine or the like comprises a plurality of collets, each for supporting and selectively grasping a tool holder mechanism. Each of the collets is slotted in its upper and central portions to divide the collet into a plurality of arcuate sections. The central portion of each collet is of generally truncated cone-shaped configuration, and rests in a generally truncated cone-shaped bore in a collet support block. A pneumatic piston arrangement is connected to the collets for selectively pulling the collets downwardly in their respective collet support blocks to move the generally arcuate sections of each collet radially inwardly to grasp a tool holder mechanism. Spring return means are provided for moving the collets into their normal positions wherein they will support, but will not grasp the tool holder mechanisms.