PURPOSE: To contrive the improvement of economical efficiency, smallness in size and the lightness in weight by forming a fold part of L-shaped section in one side part or in the peripheral part of a base board, for a tooth part to be formed, and the tooth part in the fold part by forging.

CONSTITUTION: A fold part 21 of L-shaped section is formed by press molding in the periphery of a plate-shaped tooth main unit 20, and a tooth part 22 is formed by cold forging in this fold part. Accordingly, width of the tooth part can be increased even when a plate thickness is decreased of a base board, and a gear can be formed small in size and light in weight, while enabling economical efficiency to be improved.