This copper alloy for electronic or electric devices contains 100 mass ppm or greater and 400 mass ppm or less of Mg, 5 mass ppm or greater and 20 mass ppm or less of Ag, and less than 5 mass ppm of P with a balance being Cu and inevitable impurities, in which when a ratio of J3, in which all three grain boundaries constituting a grain boundary triple junction are special grain boundaries, to all grain boundary triple junctions is defined as NFJ3 and a ratio of J2, in which two grain boundaries constituting a grain boundary triple junction are special grain boundaries and one grain boundary constituting the grain boundary triple junction is a random grain boundary, to all grain boundary triple junctions is defined as NFJ2, an expression of 0.22