PURPOSE: To enable a small-sized spindle with small rigidity to be used in a cam lathe, so as to provide a small-sized lathe by introducing a pressure compensating mechanism on the anti-cam surface side of a crown cam.

CONSTITUTION: The compensating pressure whose magnitude is determined by the shape of the cam surface of a compensating cam 11 and also by the initial displacement of a compensating spring 12, is applied to a crown cam 3 from the anti-cam surface side. Due to this pressure, the pressing force of a compressing spring 9 is cancelled out and accordingly, the force exerted from the crown cam 3 to a lathe spindle 4 becomes approximately zero all the time. Thus, a lathe spindle with low rigidity can be used as the lathe spindle 4. As a result, small- sized spindle 4 and its bearing mechanism can be employed and the construction of the lathe itself can be small-sized.