A machine reamer has a plurality of slender blades erected on the outer peripheral part of a reamer head body. Each blade of a pair of blades facing each other in a radial direction are different in material kind from each other. One of the blades treated as a pair is made of super-hard alloy and the other blade is made of one kind of material selected from the group of sintered ceramic, cermet, and microcrystalline diamond sintered material.