A Ni-based forged alloy article, comprising crystal grains of a γ phase and precipitation particles of a γ' phase, and having a chemical composition enabling to precipitate the γ' phase in an amount of 50 to 70 volume % at 700°C within a matrix of the γ phase, wherein the chemical composition consists of: 4.0 to 18 mass % of Cr; 2.0 to 25 mass % of Co; 14 mass % or less of W; 8.0 mass % or less of Mo; 2.0 to 7.0 mass % of Al; 8.0 mass % or less of Ti; 10 mass % or less of Ta; 3.0 mass % or less of Nb; 3.0 mass % or less of Hf; 2.0 mass % or less of Re; 2.0 mass % or less of Fe; 0.1 mass % or less of Zr; 0.001 to 0.15 mass % of C; 0.001 to 0.1 mass % of B; and a balance, the balance consisting of Ni and inevitable impurities, wherein the impurities include 0.01 mass % or less of Si, 0.02 mass % or less of Mn, 0.01 mass % or less of P, 0.01 mass % or less of S, 0.005 mass % or less of 0, and 0.005 mass % or less of N, and a value P represented by a formula: "value P = 0.18 × Al-content + 0.08 × Ti-content + 0.03 × Ta-content" being equal to or more than 1.0; wherein the γ' phase comprises: aging precipitation γ' phase particles precipitating within the crystal grains of the γ phase; and eutectic reaction γ' phase particles precipitating between/among the crystal grains of the γ phase, wherein the eutectic reaction γ' phase particles precipitate in an amount of 1 to 15 volume %, wherein the eutectic reaction γ' phase particles comprise a higher content of Ni and Al than the aging precipitation γ' phase particles and have an average particle size of 2 to 40 μm, and the γ phase has an average grain size of 15 to 200 μm, said average particle size and said average grain size being measured using a scanning electron microscope-energy dispersive X-ray spectroscopy analyzer, and wherein the Ni-based forged alloy article has a tensile strength in conformity with JIS Z 2241 of equal to or more than 1,200 MPa at room temperature and a creep rupture time of equal to or more than 100 hours at 780°C at a stress of 500 MPa. 4.0 to 18 mass % of Cr; 2.0 to 25 mass % of Co; 14 mass % or less of W; 8.0 mass % or less of Mo; 2.0 to 7.0 mass % of Al; 8.0 mass % or less of Ti; 10 mass % or less of Ta; 3.0 mass % or less of Nb; 3.0 mass % or less of Hf; 2.0 mass % or less of Re; 2.0 mass % or less of Fe; 0.1 mass % or less of Zr; 0.001 to 0.15 mass % of C; 0.001 to 0.1 mass % of B; and a balance, the balance consisting of Ni and inevitable impurities, wherein the impurities include 0.01 mass % or less of Si, 0.02 mass % or less of Mn, 0.01 mass % or less of P, 0.01 mass % or less of S, 0.005 mass % or less of 0, and 0.005 mass % or less of N, and a value P represented by a formula: "value P = 0.18 × Al-content + 0.08 × Ti-content + 0.03 × Ta-content" being equal to or more than 1.0; aging precipitation γ' phase particles precipitating within the crystal grains of the γ phase; and eutectic reaction γ' phase particles precipitating between/among the crystal grains of the γ phase, wherein the eutectic reaction γ' phase particles precipitate in an amount of 1 to 15 volume %, wherein the eutectic reaction γ' phase particles comprise a higher content of Ni and Al than the aging precipitation γ' phase particles and have an average particle size of 2 to 40 μm, and the γ phase has an average grain size of 15 to 200 μm, said average particle size and said average grain size being measured using a scanning electron microscope-energy dispersive X-ray spectroscopy analyzer, and wherein the Ni-based forged alloy article has a tensile strength in conformity with JIS Z 2241 of equal to or more than 1,200 MPa at room temperature and a creep rupture time of equal to or more than 100 hours at 780°C at a stress of 500 MPa. <EOS>