High quality diamond can be produced at high speed and at a low cost by a hot-filament assisted CVD method. This process comprises using a heating body consisting of a metal or metal carbide as an excitation source, wherein the heating body has a larger specific surface area (surface area/volume) than a filament with a circular cross-section for the same cross-sectional area. For example, the heating body is composed of a bundle of at least two linear heating bodies or at least two linear heating bodies twisted around each other.
