To provide a high-strength heat-resistant Ni-based forged alloy in which each crystal grain size of a polycrystal is made large so as to increase the strength of creep, and simultaneously, deterioration in the ductility of the polycrystal is suppressed, and to provide a method for producing the same.

The Ni-based forged superalloy has a composition comprising 0.005 to 0.2% C, 0 to 1% Si, 0 to 1% Mn, 10 to 24% Cr, at least one kind selected from Mo and W by 5 to 17% in the provision of [Mo concentration]+0.5[W concentration], 0.5 to 2% Al, 1 to 3.5% Ti, 0 to 10% Fe and at least one kind selected from 0.002 to 0.02% B and 0.01 to 0.2% Zr, and the balance Ni of 48 to 80% with inevitable impurities. The superalloy is composed of a polycrystal, and the average grain size of the crystals after heat treatment is 72 to 289 μm. In the superalloy, a plurality of precipitates are precipitated along crystal grain boundaries after the heat treatment, and the average length of the precipitated in the optional cross-section of the polycrystal is 0.5 to 2.5 μm.