PURPOSE: To provide a method for synthesizing diamond by which excellent mass productivity is ensured and a diamond layer can be formed only on a prescribed part.

CONSTITUTION: Chips 1 are piled up on a sample stand 2 set in the reactor of a microwave plasma CVD device so that the corners 11 of the chips 1 do not overlap each other, gaseous starting material such as gaseous CO+H2 is fed into the reactor at a high temp. under reduced pressure and a transfer mechanism is actuated so that the corners 11 of the chips 1 exist successively for a prescribed time in a region with plasma emitted by irradiation with microwaves or other method.