This ring-shaped disk for a gas turbine includes a ring-shaped disk material consisting of a Ni-based alloy, wherein the Ni-based alloy has a composition that includes, in terms of percent by mass, Ni: 50.00 to 55.00%, Cr: 17.0 to 21.0%, Nb: 4.75 to 5.60%, Mo: 2.8 to 3.3%, Ti: 0.65 to 1.15%, Al: 0.20 to 0.80%, and C: 0.01 to 0.08%, with the balance being Fe and inevitable impurities, and has a microstructure in which δ phase particles are distributed in a matrix thereof, and wherein, in the microstructure, flattened δ phase particles of which maximum length directions are oriented at angles within a range of 60 to 120° with respect to a radial direction of the ring-shaped disk material are present in an amount of 60% or more of a total amount of the δ phase particles distributed in the matrix.