An electroslag welding wire containing, by mass% based on total mass of the wire: C: more than 0% and 0.07% or less; Si: more than 0% and 0.50% or less; Mn: more than 0% and 1.0% or less; Ni: 6.0 to 15.0%; Fe: 79% or more, and optionally at least one element selected from the group consisting of Cu, Cr, Mo, W, Nb, V and B, and satisfying the following relationship: 0.150 ≤ C + Si / 30 + W / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + Nb / 10 + V / 10 + 5 × B ≤ 0.300 the electroslag welding wire further optionally containing at least one element selected from the group consisting of Ca, Mg, REM, Zr, Al and Ti, and satisfying the following relationship: 0.001 ≤ 1.6 Ca + Mg + 1.25 REM + Zr + Al + 0.8 Ti ≤ 0.70 and optionally, when the wire is a flux cored wire, the flux containing: a metal-based flux satisfying the aforementioned ranges of the composition; and a slag forming agent in an amount of more than 0% and not more than 15% based on total mass of the wire, wherein the slag forming agent contains at least one selected from the group consisting of SiO 2, CaO, CaF 2, BaF 2, MgO, Al 2 O 3, MnO, TiO 2, ZrO 2, FeO, Na 2 O, K 2 O, and BaO, and satisfies the following relationship: CaO + CaF 2 + BaF 2 + MgO + BaO + Na 2 O + K 2 O / SiO 2 + 0.5 Al 2 O 3 + TiO 2 + ZrO 2 + MnO + FeO ≥ 1.00 wherein the left side is taken as >100 when the slag forming agent does not contain any of SiO 2, Al 2 O 3, TiO 2, ZrO 2, MnO and FeO, the remainder of the electroslag welding wire being inevitable impurities. C: more than 0% and 0.07% or less; Si: more than 0% and 0.50% or less; Mn: more than 0% and 1.0% or less; Ni: 6.0 to 15.0%; Fe: 79% or more, and optionally at least one element selected from the group consisting of Cu, Cr, Mo, W, Nb, V and B, and satisfying the following relationship: 0.150 ≤ C + Si / 30 + W / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + Nb / 10 + V / 10 + 5 × B ≤ 0.300 the electroslag welding wire further optionally containing at least one element selected from the group consisting of Ca, Mg, REM, Zr, Al and Ti, and satisfying the following relationship: 0.001 ≤ 1.6 Ca + Mg + 1.25 REM + Zr + Al + 0.8 Ti ≤ 0.70 and optionally, when the wire is a flux cored wire, the flux containing: a metal-based flux satisfying the aforementioned ranges of the composition; and a slag forming agent in an amount of more than 0% and not more than 15% based on total mass of the wire, wherein the slag forming agent contains at least one selected from the group consisting of SiO 2, CaO, CaF 2, BaF 2, MgO, Al 2 O 3, MnO, TiO 2, ZrO 2, FeO, Na 2 O, K 2 O, and BaO, and satisfies the following relationship: CaO + CaF 2 + BaF 2 + MgO + BaO + Na 2 O + K 2 O / SiO 2 + 0.5 Al 2 O 3 + TiO 2 + ZrO 2 + MnO + FeO ≥ 1.00 wherein the left side is taken as >100 when the slag forming agent does not contain any of SiO 2, Al 2 O 3, TiO 2, ZrO 2, MnO and FeO, a metal-based flux satisfying the aforementioned ranges of the composition; and a slag forming agent in an amount of more than 0% and not more than 15% based on total mass of the wire, wherein the slag forming agent contains at least one selected from the group consisting of SiO 2, CaO, CaF 2, BaF 2, MgO, Al 2 O 3, MnO, TiO 2, ZrO 2, FeO, Na 2 O, K 2 O, and BaO, and satisfies the following relationship: CaO + CaF 2 + BaF 2 + MgO + BaO + Na 2 O + K 2 O / SiO 2 + 0.5 Al 2 O 3 + TiO 2 + ZrO 2 + MnO + FeO ≥ 1.00 wherein the left side is taken as >100 when the slag forming agent does not contain any of SiO 2, Al 2 O 3, TiO 2, ZrO 2, MnO and FeO, the remainder of the electroslag welding wire being inevitable impurities.