To prevent a material from being scored at the time of chamfering to make a fine chamfered finish by bending a flat-surface base plate at a designated angle, and cutting out the bent part to form a slit of a designated space.

A material O is adjusted to the bent angle part of a base plate 1 of a chambering support tool G. They are placed on a placing table of a chamfering machine, and pushed toward a cutter B by hand. At this time, the base plate 1 and the material O are pressed by one hand not to be separated, and pushed forward by the other hand. The corner of the material O is exposed through a slit 2 formed between a base plate 11 and a base plate 12, so that the corner part is cut by a cutter B of the chamfering machine to perform chamfering. During the operation, the surface of the material O is protected by the base plates 11, 12, so that even if the placing table of the chamfering machine is scored, the material is not damaged by the score to make a fine chamfered finish.