Ceramic-based substrate for coating, e.g., diamond has a basic irregularities surface having a surface roughness Rz of 2 to 20 .mu.m, with Rz at angle regions of 40% or more of that for other than the angle regions. The basic irregularities surface has micro-sized irregularities on an order of crystal grains constituting the uppermost surface (0.5 to 10 .mu.m), forming dual irregularities surface structure. Coating layer engages with surface irregularities to secure firm adhesion at the cutting edge. WC-based cemented carbide is used as substrate and N-containing surface layer is formed by heat treatment to form the surface irregularities.