The present invention relates to a two chamber molten metal holding furnace for low-pressure casting for manufacturing a cast product of an aluminum alloy or the like, and the purpose of the present invention is to prevent releasing of pressurized gas into molten metal and formation of bubbles in the event of intrusion of the pressurized gas into the material constituting a molten metal storage container. The area corresponding to a pressurization chamber (22) excluding a pressurization pipe (48) and a tapping pipe (50) is opened to the atmosphere via a ventilation gap (66) that is positioned higher than a fixed molten metal surface position (L3). The ventilation gap (66) is positioned higher than the fixed molten metal surface position (L3). Even when the pressurized gas has exuded into the material constituting the molten metal storage container (12) through cracks and fissures subsequently formed in the pressurization pipe or through a preexisting minute gap in the pressurization pipe, the pressurized gas is released to the outside of the furnace from the ventilation gap (66).
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