A high-tensile copper alloy for current conduction and having superior flexibility is disclosed. The hightensile copper alloy, in a first embodiment, is consisting essentially of: from 2.0 to 4.0% by weight of Ni; from 0.4 to 1.0% by weight of Si; from 0.05 to 0.3% by weight of In; from 0.05 to 0.3% by weight of Sn; and the balance of Cu. The high-tensile copper alloy, in a second embodiment, is consisting essentially of: from 2.0 to 4.0% by weight of Ni; from 0.4 to 1.0% by weight of Si; from 0.05 to 0.3% by weight of In; from 0.01 to 0.2% by weight of Co; and the balance of Cu. The high-tensile copper alloy, in a third embodiment, is consisting essentially of: from 2.0 to 4.0% by weight of Ni; from 0.4 to 1.0% by weight of Si; from 0.05 to 0.3% by weight of In; from 0.01 to 0.3% by weight of Mg; and the balance of Cu. The high-tensile copper alloy, in a fourth embodiment, is consisting essentially of: from 2.0 to 4.0% by weight of Ni; from 0.4 to 1.0% by weight of Si; from 0.05 to 0.25% by weight of In; from 0.05 to 0.25% by weight of Sn; from 0.05 to 0.20% by weight of Mg; and the balance of Cu. The hightensile copper alloy, in the fifth embodiment, is consisting essentially of: from 2.0 to 4.0% by weight of Ni; from 0.4 to 1.0% by weight of Si; from 0.05 to 0.25% by weight of In; from 0.05 to 0.20% by weight of Co; from 0.05 to 0.20% by weight of Mg; and the balance of Cu.