A copper alloy according to the present invention comprises 17 to 34 mass% of Zn, 0.02 to 2.0 mass% of Sn, 1.5 to 5 mass% of Ni and a remainder made up by Cu and unavoidable impurities, wherein the relationships represented by the formulae mentioned below are satisfied: 12 = f1 = [Zn]+5�[Sn]-2�[Ni] = 30, 10 = [Zn]-0.3�[Sn]-2�[Ni] = 28, 10 = f3 = {f1�(32-f1)�[Ni]}1/2 = 33, 1.2 = 0.7�[Ni]+[Sn] = 4 and 1.4 = [Ni]/[Sn] = 90. The copper alloy has an electric conductivity of 13 to 25% IACS or less, and the occupation ratio of an a phase is 99.5% by area or more or the area ratio (?) (%) of a ? phase and the area ratio (�) (%) of a � phase in the a phase matrix have a relationship represented by the formula: 0 = 2�(?)+(�) = 0.7.
