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Japan Atomic Energy Agency has developed Nb3Sn strands for the ITER magnet, whose critical current density is about 1.4 times as large as that of ITER CS Model Coil. The magnetic field, temperature, and strain dependence on the critical current (Ic) of the strands were measured with apparatus that were developed by the authors. The strain properties in particular were investigated in detail, with strain tensor analysis revealing that the upper critical field dependence on strain can be naturally formulated using a high order polynomial terms of strain taking into account residual strain due to thermal contraction difference inside the strand and strain applied externally. A correlation formula for field, temperature, strain and Ic of the strand is discussed and presented. Recent results of fabricating strands for ITER TF coil are then finally provided.