PURPOSE:To enable the automatic replacement of a collet chuck and save energy by providing a collet having a grip groove for the gripper of a robot hand, etc., a collet engaging part, an engageable and removable claw body, and their driving means. CONSTITUTION:When a draw tube 4 is drawn by means of a driving device, the taper 5a of a collet 5 becomes an open condition being released from a taper hole. Then, when a pressure air is sent to the front chamber 7b of a cylinder 7, causing a piston 8 to be retracted to a main spindle side against a compression spring 17, a claw body 6 is outwardly moved by means of a bell crank lever 12 removing the engaging part 6a of the claw body 6 from the engaging part 5c of the collet 5. And, a collar 10 connected to the piston 8 is retracted, an approaching switch 16 is operated by means of a dog 11 and, due to an output signal and by means of a replacing arm of a robot or an ATC, a desired collet which is gripped out from a stocker, etc., is positioned in a replacing position, while the collet 5 is taken out with its grip groove 54 being gripped by another empty gripper, and the new collet is inserted and fixed.
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