A metal-joining structure (100) includes: an iron alloy part (1); an aluminum alloy part (2); and a joining interface layer (3) provided between the iron alloy part (1) and the aluminum alloy part (2). The joining interface layer (3) includes: an iron-silicon solid-solution-phase sublayer (4) in contact with the iron alloy part (1); an aluminum-silicon eutectic-phase sublayer (5) in contact with the aluminum alloy part (2); and a silicon sublayer (6) provided between the iron-silicon solid-solution-phase sublayer (4) and the aluminum-silicon eutectic-phase sublayer (5).