The present invention relates to a Ni-based heat-resistant alloy including Ir: 5.0 mass % or more and 50.0 mass % or less, Al: 1.0 mass % or more and 8.0 mass % or less, W: 5.0 mass % or more and 25.0 mass % or less, and balance Ni, having an L12-structured γ′ phase present in the matrix, and including at least one of Ru: 0.8 mass % or more and 5.0 mass % or less and Re: 0.8 mass % or more and 5.0 mass % or less. This Ni-based heat-resistant alloy has improved toughness over a conventional Ni-based heat-resistant alloy based on a Ni—Ir—Al—W-based alloy, and is also excellent in ambient-temperature strength.