In a grain milling machine, a milling chamber 25 is defined by a gap between a cylindrical body 24 and a rotating body 23, and grinding plates 27 and 28 are arranged on both facing surfaces of the milling chamber 25. On the surface of at least one of the grinding plates 27 and 28, polyhedral hard diamond abrasive grains are deposited. The grinding plate 27 provided on the side of the cylindrical body 24 is fixed, and the grinding plate 28 provided on the side of the rotating body 24 moves with respect to the grinding plate 27, so that the surfaces of grains fed into the milling chamber 25 are ground by the grinding function applied between the grinding plates 27 and 28. Thus, it is possible to maintain sufficient grinding force and to carry out efficient and high-quality grain milling without the need of any complicated maintenance of the machine.