To provide a molten magnesium supply pump having a high accuracy in molten metal supply.

A vane type molten metal pump 106 transports molten magnesium 114 stored in a vessel 104 to a runner pipe 102. A control unit 120 changes the number of revolutions of a rotor according to the height of the molten magnesium 114 within the vessel 104. The control unit 120 performs an intermittent operation in which an operation period of time during which the rotor is rotated for a predetermined time and a stop period of time during which the rotor is stopped are repeated alternately, and increases the number of revolutions of the rotor each time the operation period of time is performed. The control unit 120 determines a number N of revolutions so as to satisfy a relation: Δh=a×N²+b (where a and b denote parameters of real number) when the difference between a molten metal height H as a reference and a present molten metal height h is Δh.