A tape-shaped superconducting film-forming substrate is disclosed, which includes a film-forming face for forming a laminate including a superconducting layer thereon, a rear face that is a face at a side opposite to the film-forming face, a pair of end faces connected to the film-forming face and the rear face, and a pair of side faces connected to the film-forming face, the rear face, and the pair of end faces, in which each of the pair of side faces includes a spreading face that spreads toward an outer side in an in-plane direction of the film-forming face from an edge part of the film-forming face toward the rear face side. A superconducting wire and a superconducting wire manufacturing method are also disclosed.