PURPOSE: To polish a metal belt in an highly accurate manner, by stirring the belt metal, which is used for a carriage assembly of a magnetic recording reproducer, inside a mixed vessel containing an abrasive, water and a compound material, so as to become a specified capacitance ratio, and polishing it in this way.

CONSTITUTION: A metal belt 1, consisting of stainless steel as material, is one that forms an overhanging part 3 having each through hole 2 at both sides and the central part, and performs the following facing operations as its deburring finish. That is to say, abrasives 5 are put in mixing vessel 4, while unprocessed metal belts 1 being formed into four groups - 75 pieces at each group - are put in a side wall part inside this mixing vessel 4 as opposed with one another at equiangularity. And, water 6 of 75W85%, inclusive of these abrasives, to capacity of the mixed vessel 4 is put in the mixing vessel 4 and furthermore a compound material of more than 0.25% in the total capacitance ratio is put in this vessel. After that, the whole vessel 4 is rotated after covering it with a lid 7, thus the metal belt is polished.