To provide a chuck apparatus for holding a workpiece as a metal shaft material or a metal tube material in a shaft enlarging machine, wherein the workpiece is simply taken out from a sleeve and also, even in the case of being the workpiece having an enlarged part, the workpiece can simply and surely be held.

In a hollowing part of the chuck body, the sleeve composed of a plurality of sleeve pieces having a holding groove for holding the workpiece, is engaged under state of forming one holding hole with the holding groove, and the sleeve is slid in the axial direction of the hollow part of the chuck body and also, the sleeve is not taken off from the chuck body by rotating a cam shaft arranged so as to be rotatable to the chuck body to hang the cam piece of the cam shaft to the groove part arranged on the sleeve piece. Further, tapered parts are arranged in the hollow part of the chuck body and the sleeve piece of the sleeve, and the sleeve is slid along the tapered part of the chuck body with the operation of the cam shaft, so as to surely hold the workpiece with the holding groove.