A superconductivity stabilizing material used for a superconducting wire, consisting of a copper material containing at least one of additive elements selected from Ca, Sr, Ba, and rare earth elements in a range of 3 ppm by mass or more and 100 ppm by mass or less in total, with a remainder being Cu and unavoidable impurities, wherein a total concentration of the unavoidable impurities, excluding O, H, C, N, and S which are gas components, is 5 ppm by mass or more and 100 ppm by mass or less, the residual resistance ratio, RRR, is 50 or more and 500 or less, and characterised in that the half-softening temperature is 200°C or lower, the Vickers hardness is 55 Hv or more, and the half-softening temperature is defined as follows: the Vickers hardness at room temperature after cold plastic working with an area reduction rate of 50% or more or a rolling rate of 50% or more is set as Hv_, the area reduction rate = (cross-sectional area before wire drawing - cross-sectional area after wire drawing) / (cross-sectional area before wire drawing) x 100, the rolling rate = (thickness before rolling - thickness after rolling) / (thickness before rolling x 100, the Vickers hardness measured at room temperature after rapid cooling after holding for one hour in an Ar gas atmosphere at 500°C is set as Hv_500°C, Hv _ recry = Hv_ 500 ∘ C + Hv_ CD − Hv_ 500 ∘ C / 2, the heat treatment temperature before rapid cooling when the hardness is Hv_recry is set as the half-softening temperature. a total concentration of the unavoidable impurities, excluding O, H, C, N, and S which are gas components, is 5 ppm by mass or more and 100 ppm by mass or less, the residual resistance ratio, RRR, is 50 or more and 500 or less, and characterised in that the half-softening temperature is 200°C or lower, the Vickers hardness is 55 Hv or more, and the half-softening temperature is defined as follows: the Vickers hardness at room temperature after cold plastic working with an area reduction rate of 50% or more or a rolling rate of 50% or more is set as Hv_, the area reduction rate = (cross-sectional area before wire drawing - cross-sectional area after wire drawing) / (cross-sectional area before wire drawing) x 100, the rolling rate = (thickness before rolling - thickness after rolling) / (thickness before rolling x 100, the Vickers hardness measured at room temperature after rapid cooling after holding for one hour in an Ar gas atmosphere at 500°C is set as Hv_500°C, Hv _ recry = Hv_ 500 ∘ C + Hv_ CD − Hv_ 500 ∘ C / 2, the heat treatment temperature before rapid cooling when the hardness is Hv_recry is set as the half-softening temperature. the Vickers hardness at room temperature after cold plastic working with an area reduction rate of 50% or more or a rolling rate of 50% or more is set as Hv_, the area reduction rate = (cross-sectional area before wire drawing - cross-sectional area after wire drawing) / (cross-sectional area before wire drawing) x 100, the rolling rate = (thickness before rolling - thickness after rolling) / (thickness before rolling x 100, the Vickers hardness measured at room temperature after rapid cooling after holding for one hour in an Ar gas atmosphere at 500°C is set as Hv_500°C, Hv _ recry = Hv_ 500 ∘ C + Hv_ CD − Hv_ 500 ∘ C / 2, the heat treatment temperature before rapid cooling when the hardness is Hv_recry is set as the half-softening temperature.