A heat-resistant
alloy spring is made of a Ni-based
alloy material comprising in weight %: not more than 0.1% C; not more than 1.0% Si; not more than 1.50% Mn; 13.0 to 25.0% Cr; 1.5 to 7.0% Mo; 0.5 to 4.0% Ti; 0.1 to 3.0 % Al; {at least one optional element selected from the group consisting of 0.15 to 2.50% w, 0.001 to 0.020% B, 0.01 to 0.3% Zr, 0.30 to 6.00% Nb, 5.0 to 18.0% Co, and 0.03 to 2.00% Cu}; the balance being essentially Ni; and incidental impurities. The Ni-based
alloy material is provided in its
crystal structure with gamma prime phase [Ni3(Al, Ti)] or gamma prime phase [Ni3(Al, Ti, Nb)]. The gamma prime phase has an average grain
diameter (d) of not less than 25 nanometers, and a
hardness-
diameter ratio (Hv / d) of a Vickers
hardness Hv of a position at a depth of one-fourth of the entire thickness or the wire
diameter from a surface of the Ni-based alloy material toward its center and the average grain diameter d(nanometer) is 5 to 25. The Ni-based alloy wire used as the Ni-based alloy material has a Hv
hardness of 320 to 480 and a longitudinal
elastic modulus of 150,000 to 230,000 N / sq.mm.