An object of the present invention is to effectively reduce mixing of bubbles into a spun glass fiber. A glass-melting device 10 for producing glass fibers includes; a first glass-melting tank 12 exposed to a reduced-pressure atmosphere; a second glass-melting tank 14 and a third glass-melting tank 16 arranged below the first glass-melting tank 12; an ascending conduit 18 that sends up molten glass resulting from melting in the second glass-melting tank 14 to deliver the molten glass to the first glass-melting tank 12; a descending conduit 20 that sends the molten glass down from the first glass-melting tank 12 to deliver the molten glass to the third glass-melting tank 16; a decompression housing 22; and a bushing 24. The glass-melting device 10 further includes heating means for separately heating the first glass-melting tank 12, the second glass-melting tank 14, the third glass-melting tank 16, the ascending conduit 18, the descending conduit 20 and the bushing 24.