There are provided high-strength and high-toughness heat-resistant cast steels applicable to steam turbine casings, precision cast vanes and valves. There is disclosed a high-strength and high-toughness heat-resistant cast steel formed of a heat-resistant cast steel consisting of, based on weight percentage: 0.08 to 0.25% of carbon; more than 0.1 not more than 0.5% of silicon; 1% or less of manganese; 0.05 to 1% of nickel; 9 to 12% of chromium; 0.3 to 1.5% of molybdenum; 1 to 1.95% of tungsten; 0.1 to 0.35% of vanadium; 0.02 to 0.1% of niobium; 0.01 to 0.08% of nitrogen; 0.001 to 0.01% of boron; and 2 to 8% of cobalt; the balance substantially being iron; and having a martensite matrix structure.