PURPOSE: To improve polishing efficiency through cutting off of the protrusions and recesses of the inner surface of a container by a method wherein mixture magnetic grinding grains prepared by mixing together fine magnetic grinding grains and large iron powder larger than the magnetic grinding grains is charged in a position, situated facing a magnetic pole, in the container.

CONSTITUTION: Mixture magnetic grains charged in a container W are formed of mixture of magnetic grinding grains J and iron powder F larger than the magnetic grinding grains. The iron powder F is aligned and intercoupled in a chain-form manner along the direction of a line of magnetic force. Fine magnetic grinding grains J are adhered to the periphery thereof to produce a firm magnetic force holding module (polymer). The magnetic force holding module is deformed in a form where a part of the mixture magnetic grinding grains J are slipped down over a slope owing to rotation of the container W. The direction of a firm line of magnetic force is kept approximately in a constant state and a polishing pressure is continued to exert a polishing pressure on the inner surface of the container W. The polishing pressure causes cutting off of the protrusions and the recesses of the inner surface of the container W to improve polishing efficiency.