To provide a work chuck device, which apparatus does not cause the deflection of the workpiece even when the clamping force between workpiece centers is large in the case of fixing a comparatively long workpiece, such as a crankshaft, and further does not cause such a problem that the workpiece is bruised by chuck jaws owing to a too large chucking force in the case of chucking the end portion of the workpiece by means of a chuck.

The chucking apparatus comprises a natural clamping device having such a mechanism that when a crankshaft having tapered center holes on both end faces in its axial direction is held by fitting tapered centers in the center holes from both sides, and further by chucking the workpiece by moving chuck jaws, a stopper pin 30 is brought into contact with the end portion of the workpiece via a link arm engaged with one of the chuck jaws.