A free-cutting copper alloy casting comprising: 75.0 mass% to 78.5 mass% of Cu; 2.95 mass% to 3.55 mass% of Si; 0.07 mass% to 0.28 mass% of Sn; 0.06 mass% to 0.14 mass% of P; 0.022 mass% to 0.20 mass% of Pb; less than 0.06 mass% of Ni; optionally one or more element(s) selected from the group consisting of 0.02 mass% to 0.08 mass% of Sb, 0.02 mass% to 0.08 mass% of As, and 0.02 mass% to 0.30 mass% of Bi; and the balance being Zn and inevitable impurities, wherein the total amount of Fe, Mn, Co, and Cr as the inevitable impurities is lower than 0.08 mass%, when the Cu content is represented by [Cu] mass%, the Si content is represented by [Si] mass%, the Sn content is represented by [Sn] mass%, the P content is represented by mass%, and the Pb content is represented by [Pb] mass%, the relations of 76.2 ≤ f 1 = Cu + 0.8 × Si − 8.5 × Sn + P + 0.5 × Pb ≤ 80.3 and 61.2 ≤ f 2 = Cu − 4.4 × Si − 0.8 × Sn − P + 0.5 × Pb ≤ 62.8 are satisfied, in constituent phases of metallographic structure, when the area ratio of α phase is represented by (α)%, the area ratio of β phase is represented by (β) %, the area ratio of γ phase is represented by (y)%, the area ratio of κ phase is represented by (κ)%, and the area ratio of μ phase is represented by (μ)%, relative to the total area ratio of α phase, β phase, γ phase, δ phase, ε phase, ζ phase, η phase, κ phase, μ phase and χ phase, the relations of 25 ≤ κ ≤ 65, 0 ≤ γ ≤ 2.0, 0 ≤ β ≤ 0.3, 0 ≤ μ ≤ 2.0, 96.5 ≤ f 3 = α + κ, 99.2 ≤ f 4 = α + κ + γ + μ, 0 ≤ f 5 = γ + μ ≤ 3.0, and 29 ≤ f 6 = κ + 6 × γ ​ 1 / 2 + 0.5 × μ ≤ 66 are satisfied, the length of the long side of γ phase is 50 μm or less, the length of the long side of μ phase is 25 μm or less, κ1 phase is present in α phase and has a thickness of 0.05 μm to 0.5 μm, the amount of Sn in κ phase is 0.08 mass% to 0.40 mass%, and the amount of P in κ phase is 0.07 mass% to 0.22 mass%, wherein the microstructural features and the Sn and P amounts in the κ phase are determined by the methods as defined in the description. 75.0 mass% to 78.5 mass% of Cu; 2.95 mass% to 3.55 mass% of Si; 0.07 mass% to 0.28 mass% of Sn; 0.06 mass% to 0.14 mass% of P; 0.022 mass% to 0.20 mass% of Pb; less than 0.06 mass% of Ni; optionally one or more element(s) selected from the group consisting of 0.02 mass% to 0.08 mass% of Sb, 0.02 mass% to 0.08 mass% of As, and 0.02 mass% to 0.30 mass% of Bi; and the balance being Zn and inevitable impurities, wherein the total amount of Fe, Mn, Co, and Cr as the inevitable impurities is lower than 0.08 mass%, when the Cu content is represented by [Cu] mass%, the Si content is represented by [Si] mass%, the Sn content is represented by [Sn] mass%, the P content is represented by mass%, and the Pb content is represented by [Pb] mass%, the relations of 76.2 ≤ f 1 = Cu + 0.8 × Si − 8.5 × Sn + P + 0.5 × Pb ≤ 80.3 and 61.2 ≤ f 2 = Cu − 4.4 × Si − 0.8 × Sn − P + 0.5 × Pb ≤ 62.8 are satisfied, in constituent phases of metallographic structure, when the area ratio of α phase is represented by (α)%, the area ratio of β phase is represented by (β) %, the area ratio of γ phase is represented by (y)%, the area ratio of κ phase is represented by (κ)%, and the area ratio of μ phase is represented by (μ)%, relative to the total area ratio of α phase, β phase, γ phase, δ phase, ε phase, ζ phase, η phase, κ phase, μ phase and χ phase, the relations of 25 ≤ κ ≤ 65, 0 ≤ γ ≤ 2.0, 0 ≤ β ≤ 0.3, 0 ≤ μ ≤ 2.0, 96.5 ≤ f 3 = α + κ, 99.2 ≤ f 4 = α + κ + γ + μ, 0 ≤ f 5 = γ + μ ≤ 3.0, and 29 ≤ f 6 = κ + 6 × γ ​ 1 / 2 + 0.5 × μ ≤ 66 are satisfied, the length of the long side of γ phase is 50 μm or less, the length of the long side of μ phase is 25 μm or less, κ1 phase is present in α phase and has a thickness of 0.05 μm to 0.5 μm, the amount of Sn in κ phase is 0.08 mass% to 0.40 mass%, and the amount of P in κ phase is 0.07 mass% to 0.22 mass%, wherein the microstructural features and the Sn and P amounts in the κ phase are determined by the methods as defined in the description.