To provide a molten metal supply device configured to stably maintain supply amount of molten metal at a constant level.

A molten metal supply device 40 includes: a delivery part (pump driving part 41 and pressure feeding pump 42) delivering molten metal stored in a storage tank 30 so as to supply the molten metal to an inner space formed within a casting die 10 every time the casting die 10 installed in a die casting machine 1 and opened/closed is closed; a supply amount acquisition part (delivery amount control device 43 and linear encoder 44) acquiring biscuit thickness t that is amount indicating the supply amount of the molten metal supplied to the inner space of the casting die 10; and a delivery amount correction part (delivery amount control device 43) correcting delivery amount of the molten metal delivered by the delivery part so that the supply amount of the molten metal supplied to the inner space falls within a preset range, on the basis of the amount indicating the supply amount of the molten metal acquired by the supply amount acquisition part.