The following are disclosed: A method for synthesis of diamond which is characterized by contacting a gas obtained by excitation of carbon monoxide and hydrogen in such a ratio as carbon monoxide being at least 1 mol% per total of carbon monoxide and hydrogen with a substrate in the presence of a reducing metal. A method for synthesis of diamond which is characterized by contacting with a substrate a gas obtained by excitation of carbon dioxide and hydrogen mixed at such a ratio of carbon dioxide being 0.1-20 mol% per hydrogen. A method for synthesis of diamond by depositing diamond on the surface of a substrate by introducing onto the surface of the substrate a plasma obtained from hydrogen and carbon source gas by irradiation of microwave in a plasma generator which is characterized in that progress of microwave oscillated from one microwave oscillator is divided and thus divided respective microwaves and led to a plurality of plasma generators. A diamond synthesis apparatus which is characterized by comprising a microwave oscillator for oscillation of microwave, a branched waveguide for dividing the microwave oscillated from said microwave oscillator and a plurality of plasma generators which are connected with said branched waveguide and have a substrate for deposition of diamond, respectively.
