Theoretical studies of variations in the critical current I_c under bending conditions are carried. In Nb₃Sn conductors produced by solid state diffusion process, the matrix (bronze) is subjected to a tensile stress, because bronze contracts stronger than Nb or Nb₃Sn during cooling from the diffusion temperature to 4K. This tensile prestrain makes the stress-strain curve for the bronze be unbalanced about the origin of the σ-ε coordinates upon bending. Thus, during bending, the bronze on the tension side will reach the yield strain earlier than will the bronze on the compression side. This results in shifting of the neutral axis from the center of the conductor toward the center of curvature. The amount of the shiftng are theoretically calculated. Using the results, the critical current dependence on the bending strain and the maximum real tensile strains in Nb₃Sn in bending test are estimated. Those results are compared with the experimental results and they are agreed each other well. It is also shown that the real tensile strain becomes larger than the simply added strain of the tensile one and the bending one when both strain work together.