PURPOSE: To efficiently manufacture an Au alloy material excellent in quality by casting an Au alloy material into a round shape and working it into a square shape.

CONSTITUTION: A high frequency vacuum molten Au alloy is cast into a round shape. Next, this alloy is worked into a square shape by a grooving roll. Then, it is annealed and is thereafter subjected to finish working into a square bar by a grooving roll. As for one embodiment in this invention, explanation will be given. High frequency vacuum melting is executed to 3kg of K18 (75% Au, 12.5% Ag and 12.5% Cu) to cast into a round shape having 55cm diameter and 200mm length. Next, as is in a round casting, it is formed into a square bar having 20mm length per side and 500mm square length by a grooving roll. Then, it is annealed at 650°C for 30min and is thereafter subjected to finish working into a square bar having 8mm length per side and having 3000mm square length. In this way, the generation of the objective Au alloy material is prevented, and the process can be reduced.