To provide a mechanism for offsetting bend deflection of a tool shaft supported in cantilever, which is generated in accordance with clamping force generated in an internal gear rolling machine having the tool shaft.

Stress and positional information at two axial-direction points of the tool shaft 2 are always monitored and necessary positional relationship between the above two points is instantaneously maintained with numerically controlled pistons 12, 32 in disposed two places. By such a control, the programmed operation can be employed in operation for holding parallelism between the shaft of the gear 4 to be worked and the tooth part 21 of the tool regardless of clamping force, or operation for forming crowning on the gear to be worked by consciously inclining the tool shaft 2 in the final stage of the form rolling, or the like.