To reduce the emissions of carbon dioxide while efficiently generating molten metal by performing melting by direct flame of a burner and heat-retention of the molten metal by an electric heater etc., and to elongate the service life of the heater.

This metal melting furnace includes: a molten metal heat retaining device 100 having a crucible storage casing 130 storing the crucible 110 to form a heat retention space 160 between the crucible storage casing 130 and an outer wall of the crucible 110 to which metal 400 to be molten (ingot) is charged and which holds molten metal in the heat retention state and the heater 180 provided on the inner wall of the crucible storage casing 130 and used for maintaining the molten metal within the crucible 110 at predetermined temperature; and a combustion device 200 having a combustion device casing 210 attachable/detachable to/from the upper end of the crucible storage casing 130 and forming a combustion chamber 250 between the combustion device casing 210 and an upper end opening 112 of the crucible 110 while fitted to the upper end of the crucible storage casing 130 and the burner 220 for melting the metal 400 to be molten charged to the crucible 110 by direct flame.