To solve the problem in a grinder and a conventional kitchen knife grinder wherein a cutter is easy to rebound from a rotary polishing body and an angle for polishing the cutter is difficult to be stabilized.

This polishing machine includes a polishing body having a pair of polishing surfaces at both ends of a rotary shaft performing a rotating motion, a pair of side surface plates facingly provided to each of the pair of polishing surfaces and a casing provided to wrap the polishing body and the side surface plates, for polishing the cutter. A pair of guide grooves are provided between the respective pair of polishing surfaces and the pair of side surface plates. When the cutter is inserted into the guide grooves, the cutter is pressed by the side surface plates.