Abstract: In the ink jet printer using hot melt ink, a heater is provided for overheating hot melt ink in the ink supply channel. The collector is provided for collecting air bubbles generated when the hot melt ink is overheated by the heater. The air bubbles, collected in the collector, are then expelled from the release valve. The hot melt ink is subsequently cooled before the ink enters the print head section, where the air is dissolved in the ink. The above-described air bubble-releasing and -dissolving processes are repeatedly performed as the ink is circulated due to the maintained difference in ink level between the ink supply chamber and the ink collecting chamber.