A precursor for fabricating a Nb3Sn superconducting wire by an internal Sn process includes one or a plurality of stabilizing copper portions collectively disposed in the center, each stabilizing copper portion being provided with a diffusion barrier layer in the periphery thereof, and a superconducting matrix portion disposed so as to surround the one or the plurality of stabilizing copper portions, the superconducting matrix portion including a Nb or Nb-based alloy core and a Sn or Sn-based alloy core embedded in a Cu or Cu-based alloy matrix.