The pair of the lateral holder straps (51) retain two opposite edge sections of a wafer, while a pair of rear side holder straps (53), of closer configuration than the lateral ones and parallel to them, support the wafer edges. On both types of the holder straps are fitted protrusions (61) arranged in oblique configuration at a corresponding angle. Preferably the protrusions on the lateral holder straps are higher positioned by a specified amount than those on the rear side holder straps. The amount is related to the inclination angle and strap spacing.
