HEADSTOCK OF MACHINE TOOL

PROBLEM TO BE SOLVED: To improve a working accuracy by minimizing a run-out of a shaft- like work. SOLUTION: A main spindle 23 provided rotatably in a headstock of a cylindrical grinding machine has a collet chuck 48 which is opened and closed by a left and right motions of a piston 41, and a center 31 which is moved in left and right directions with respect to the collet chuck 48 by a piston 34. For clamping a shaft-like work W by a centering method, a periphery of a center head 32 of the center 31 advanced rightward is chucked by the collect chuck 48, and then the center head 32 is fitted into a center hole W1 of the shaft-like work W. For clamping the shaft-like work W by a chucking method, the center head 32 of the center 31 advanced leftward is engaged with the center hole W1 of the shaft-like work W, and then a periphery of the shaft-like work W is chucked by the collet chuck 48.