PURPOSE: To adjust pressing force distribution to a lapping bowl as well as to make a workpiece accurately machinable, by mounting a weight of almost the same diameter on the lapping bowl via a ring interposition.

CONSTITUTION: In a lapping bowl 11, a rod inserter 12 is engaged in a central sunken part 11b, and a weight 13 of almost the same diameter is mounted on the upper part by a positioning ring 15 via rubber plate 14. And, when a workpiece is machine in this lapping bowl 11, since this lapping bowl 11 is pressed by the weight 13 via the ring rubber plate 14, the pressing force is dispersed wide and thereby flat accuracy of the lapping bowl 11 is maintainable, thus lapping accuracy of finishing of the workpiece is securable. Thus, uniform pressing force against the lapping bowl is well securable with a simple structure without using any other device for hydraulic pressure or the like.