An aluminum alloy cast impeller has a stable high-temperature strength (e.g., 0.2% proof stress value of 260 MPa or more) at about 200° C. A boss part, blade parts, and a disc part have secondary dendrite arm spacings of 20 to 50 μm, 10 to 35 μm, and 5 to 25 μm, respectively, and satisfy the relationship Amax>Bmax>Cmax, where Amax, Bmax, and Cmax are the maximum values of the secondary dendrite arm spacings of the boss part, the blade parts, and the disc part, respectively. During casting, Al alloy molten metal is pressure injected into a 200 to 350° C. plaster mold. A 100 to 250° C. chill occurs on a surface in contact with an impeller disc surface, so that the chill temperature (° C.)