PURPOSE: To eliminate such a risk that a workpiece trips over or turns over in the case of the small diameter of the workpiece, by attaching the workpiece to the convex spherical surface side of a spherical bearing, and as well by applying both pressing force for lapping and driving force for sliding to the concave spherical seat side.

CONSTITUTION: The convex spherical part of a workpiece holder 17 to which a workpiece 2 is secured is fitted into the concave spherical seat of a concave spherical part 18, and a load P is applied to a loading rod 5 which is also applied with slide force by means of a drive arm 7. With respect to the sliding direction of the workpiece for lapping, indicated by the arrow A, the workpiece is stable irrespective of its shape within a range of 0≤h2-h1≤b even though the diameter (a) of the workpiece is small, where h1 is the vertical distance between the lapping surface 1 and the center point O' of the convex spherical surface of the workpiece holder 17, and h2 is the height of the action point of a resultant force F for thrusting the holder 17 from the lapping surface 1, thereby occurrence of scratches is limited to be minimum. Further, (b) is the diameter of a circular plane-projection of the holder 17.