To accomplish uniform mirror-polishing on the edge of a wafer by a method, wherein at least the edge part of a silicon wafer is treated by an etching chemical liquid having the composition which suppresses etching speed.

An edge part 13 of a wafer 10 is supported by four wafer supporting members 11 and is so constituted to have the wafer 10 rotate by a rotating mechanism. A chemical solution injection nozzle 14 is arranged above the edge part 13 of the wafer 10, and when chemical solution is dipped from the edge part 13 of the wafer 10, the edge part 13 is polished uniformly by etching because the wafer 10 is rotated by the rotating mechanism 12. An etching chemical liquid having an etching speed controlling composition, is used for etching. The etching chemical liquid, having an etching speed restrained composition, is used for etching. It is necessary that the etchant have an etching speed lower than the normal etching speed, i.e., lower than 1 μm/min., and it is more preferable to have a speed range of 0.05 to 1 μm/min.