PURPOSE: To provide a cylinder block of an internal combustion engine in which the clevis volume of a combustion chamber when a piston is located at the top dead center is made smaller than before so as to reduce the production of Nox and its finishing method as well as honing head structure used therefor.

CONSTITUTION: The surface roughness on the internal surface of a bore 5 in a first interval L1 between the top end 5A of the bore 5 and a point of the bore where the top part of a piston ring 7 at the top dead center is located and the piston ring 7 slides is formed finer than that on the internal surface of the bore 5 in a second interval L2 between the upper part of the piston ring 7 at the top dead center and the lower end 5B of the bore 5. Namely the surface roughness in the first interval L1 is made finer than that in the second interval L2 by the cylinder block of an internal combustion engine and the grinding wheel expanding pressure, grinding wheel grain, etc., of a grinding wheel 23.