PURPOSE: To eliminate concentrated load against a work thus to prevent breakdown by providing a balancer for balancing the upper and lower surface plates in parallel when the former will lower and contact against the latter in lapping machine for semiconductor wafer.

CONSTITUTION: The sun gear 14 of lower surface plate 10 is provided with a coaxial spline 18, a coupling section 19 and a supporting shaft 20 through an universal coupling and the upper plate 11 is fixed to said shaft 20. An annular groove 21 is made in the circumference of the upper face of the upper surface plate 11 and a plural balancer 22 are fixed in said groove 21. The balancer is adjusted to maintain parallelism against the lower plate 10 when supporting the upper plate 11 rollably through an union coupling while separating from the lower plate 10. Consequently, when lowering the upper plate 11 and contacting tightly against the lower plate 10, concentrated load due to shifted contact of wafer against the wedge section can be prevented resulting in prevension from breakdown.