In a hot chamber die casting apparatus of pressurizing molten magnesium alloy at an atmospheric pressure or higher without being exposed to the atmosphere and forming a magnesium alloy casting product in the shape of a mold, the hot chamber die casting apparatus basically configured with a melting furnace having a heater, a pressure unit configured to pressurize the molten magnesium alloy, and a mold configured to shape a product, and includes an electromagnetic stirrer disposed around a nozzle between a pressure chamber and the mold, and configured to stir semisolid magnesium alloy, the pressure chamber being connected to the melting furnace and supplying magnesium alloy in liquid state, wherein an inner diameter of the nozzle is partially or wholly smaller than that of the pressure chamber so as to crush solid phases existing in the semisolid magnesium alloy in the pressure chamber or the nozzle.
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