To reduce break of a cutter by containing a low Co content in the central area extending apart from the carbide-diamond interface adjacent to a diamond table, and containing a carbide with a higher Co content in the remaining part of the base material, that is, the outer area.

The core 12 of a base material 10 is manufactured from a sintered WC having 5-15 wt.% of Co binder phase. The outer part 14 of the base material 10 is manufactured from sintered WC having 13-22 wt.% of Co binder phase. A carbide which is harder or has higher rigidity is required by the core 12 of a cutter to support a diamond table 40. When softer carbide (e.g. with a higher Co content) is used in the area, the diamond table 40 is bent to propagate a vertical crack through the whole of the cutter. Thus, break and abrasion of the cutter can be reduced.