A method for manufacturing a copper alloy of the present invention is a method for manufacturing a Cu—Ni—Sn-based copper alloy and includes: a first aging treatment step of performing an aging treatment in a temperature range of 300° C. to 500° C. using a solution treated material; an inter-aging processing step of performing cold working after the first aging treatment step; and a second aging treatment step of performing an aging treatment in a temperature range of 300° C. to 500° C. after the inter-aging processing step. In the first aging treatment step, a peak aging treatment is preferably performed. In addition, in the second aging treatment step, the aging treatment is preferably performed for a short period as compared to that of the aging treatment in the first aging treatment step. In the inter-aging processing step, cold working is preferably performed at a processing rate of more than 60% to 99%.