Disclosed is an apparatus for and a method of thixocasting a cast iron, that can effectively prevent the scale from mixing in the die (cavity) thereby to obtain sound iron castings having good mechanical properties. The apparatus includes at least a pair of dies that can freely opened and closed to define a cavity to be filled under a pressure, and an injector that injects the semi-molten iron into the cavity through a hole in a gate at the entry of the cavity so as to throttle the entry. The gate is a separate member disposed at the entry of the cavity every time an injection casting operation is carried out and is taken out together with the casting after the injection casting operation.