PURPOSE: To hold a grindstone in a pressure fitting state at all times to a work face and to polish plural kinds of the work faces of different shapes by one kind of a grindstone efficiently and yet with high accuracy by providing a magnet press-fitting the grindstone to work face by energizing a holder by bending along the work face side.

CONSTITUTION: A grindstone 18 is held in the state of its press-fitting to a work face (polishing face) 2 with a holder 11 being bent in the shape coincident with a corner part by the attraction force of a magnet 16 even in case of the shape of the corner part being changed. So that, the need for using by exchanging plural kinds of grindstones is eliminated, the polishing work efficiency is improved and the manufacturing cost of a polishing tool is curtailed as well. Also, since the grindstone 18 is press-fitted to the work face 2 always by the attraction force of the magnet 16, the following-up of the grindstone 18 to the shape of the work face 2 is improved and a high polishing accuracy can be obtd.