The present invention is related to an apparatus for forming diamond via a chemical vapor deposition process using hot metal filament based on hydrogen and methane gas, and a method thereof. In particular, the present invention provides an apparatus for using the hot filament repeatedly without breakage, in comparison with the conventional apparatus that the filament is limited in one use, and a method thereof. The apparatus that the filament is limited in one use, and a method thereof. The apparatus includes a base substrate wherein diamond is synthesized by heating filament due to supply of voltage, a pair of electrodes being located above the base substrate, and a plurality of hot filaments being placed over the both electrodes. The top portion of the electrodes has a flat surface that is parallel with the filament, and the side portion has a curved surface. A plurality of filaments is smoothly hanged to both electrodes according to the flat surface and the curved surface without fixing. At the flat surface, the filament does not generate heat, so the breakage of the filament due to carburization is prevented. Furthermore, the end of each filament is weighed with individual weight in order to provide the filament with the tension by only gravitation. Even though the length of the filament is changed by temperature change during the diamond forming, the filament is not slacked between the electrodes by the tension. Therefore, by using the apparatus and the method of the present invention, the filament can be repeatedly used without breakage.