As a raw material of a copper base alloy containing at least one of 0.2 to 12 wt % of tin and 8 to 45 wt % of zinc, at least one of a copper base alloy having a large surface area and containing carbon on the surface thereof, a copper base alloy having a liquidus line temperature of 1050° C. or less, a copper base alloy surface-treated with tin, and a copper base alloy containing 20 to 1000 ppm of carbon, is used for obtaining a copper base alloy having an excellent hot workability. If necessary, when the raw material of the copper base alloy is melted, the material of the copper base alloy may be coated with a solid material containing 70 wt % or more of carbon, or 0.005 to 0.5 wt % of a solid deoxidizer having a stronger affinity with O than C with respect to the weight of the molten metal may be added to the molten metal.