To automate multi-edged rotary tool grinding by presetting feed per revolution, to which edge grinding quantity and abrasion loss of a grinding stone consumed when the edge is ground are added, and continuing feeding, after the multi-edged rotary tool has come in contact with the grinding stone, until the preset feed per revolution is reached.

A grinding method is to make a specific edge N of the multi- edged rotary tool face a grinding stone 13 in rotation, feed either the multi- edged rotary tool 13 or the grinding stone 5 to the other direction, and grind the facing edge N by making the edge N and the grinding stone 5 coming into contact with each other. Feed per revolution, to which grinding quantity needed by the edge N and the abrasion loss of the grinding stone 5 consumed when the edge N is ground are added, is preset and feeding after the multi-edged rotary tool 13 has come in contact with the grinding stone 13 is continued until the preset feed per revolution is reached.