To provide a cutter grinding auxiliary tool extremely easy in attachment-detachment, without influencing sandwiching force by a little thickness difference.

A connecting part 1 of a proper width is arranged in the center of a rectangular plate of a freely bendable synthetic resin, and a sandwiching part 2 is bilaterally symmetrically arranged on its both sides. A magnet plate 3 is fixed inside the sandwiching part 2 when bending by the center line of the connecting part 1 so that same poles are opposed to each other, and a projection 4 is bilaterally symmetrically fixed outside. Thus, a user can install the sandwiching part of an opening state in an object position of a cutter from a top part 6, and the sandwiching force is not influenced by the little thickness difference.