PURPOSE: To conduct an efficient grinding processing, by providing a biting portion and a finishing portion at an abrasive grain reamer which is used for the grinding of the bore of the cylinder block of an automobile engine, and increasing the quantity of processing without making the biting portion long.

CONSTITUTION: At this abrasive grain reamer, the twists of edge grooves 6a at a biting portion 1a are larger than those of edge grooves 6b at a finishing portion 1b, and also grains at the cutting edges 5a of the biting portion 1a are larger than those at the cutting edges 5b of the finishing portion 1b. And in this instance, cutting edges 5a, 5b are continuous to each other, and also edge grooves 6a, 6b are connected to each other. The grinding processing quantity of the biting portion 1a can be rapidly increased without changing the outer diameter size of the abrasive grain reamer by constituting the abrasive grain reamer as above.