A pair of profile wheels 14, 18 in which concavely shaped grinding surfaces 141, 181 asymmetrical to each other are opposed to each other at right angle so as to form a concavely shaped grinding surface having a substantially semi-circular section, a guide plate 13 which is mounted on a spindle 11 of an electric or air tool side of the profile wheel 14 freely rotatably for guiding a grinding direction by bringing the edge of the circular shaped member into contact with a reference face of a grinding object material and a stopper ring 16 which is mounted to a spindle between the pair of the profile wheels 14 and 18 freely rotatably for controlling a grinding distance Y from the edge by bringing its outer peripheral end face 161 into contact with the edge of the grinding object material, are fixed to the spindle 11 with a lock nut such that they are set at right angle to the spindle.