PURPOSE: To eliminate variation of accuracy due to edge error which may be produced during grinding of cutting tool in such a way that a grinder is contrived to be able to grind the cutting tool kept fitted to the main spindle, etc. of a milling machine.

CONSTITUTION: An electromagnet 3 is housed in a bed 1, the lower part of a body 4 is pivotally supported as shown by 6 to be able to be tilted on its upper side, a rotatable drum 7 is fitted to be able to freely turn at the upper part of the body 4, a motor 14 equipped with a rotary grinding stone 15 is fitted to be able to freely move in the orthogonal direction to the axial direction through a slide stand 11 at the front end of the drum 7, further the drum 7 is tightly fixed to the body 4, and the body 4 is also made to be able to be tightly fixed to the bed 1. When a cutting tool is ground, said bed 1 is put on a table near the tool to be tightly fixed by electrically conducting on the electromagnet 3, and the grinding stone 15 is tightly fixed by turning the body 4, the drum 7, etc. so as to run along the side to be machined of the tool.