To provide a method for casting an aluminum alloy having little gas content and little defect such as a blow hole, even in the state of as casting.

In a die casting method, in which after vacuum sucking a cavity 1 and making the pressure in the cavity not lower than the atmospheric pressure by pouring reactive gas into the cavity, molten aluminum alloy M is supplied into a sleeve 3 and thereafter, a molten metal is force-fed into the cavity, the aluminum alloy is melted so that the temperature of the molten metal does not exceed 800°C. After melting, degassing-treatment is performed by pouring inert gas into the molten aluminum alloy, and hydrogen gas content in the molten aluminum alloy is made to ≤0.5 cc/100 g. Thereafter, while holding the molten aluminum alloy at 650-760°C, the molten aluminum alloy is poured into the sleeve 3 in a die casting machine at inclining angle in the range of 5-45°, and then, the molten aluminum alloy is force-fed in the cavity 1 so that the passing speed of the molten aluminum alloy through a gate 2 in the die becomes 20-200 m/s.