To prevent liquid being fed into a liquid ejection head from thickening due to temperature drop in a method for sustaining liquid ejection performance of a liquid ejector for ejecting liquid supplied from a liquid container into the liquid ejection head from a liquid ejection nozzle.

In the method for sustaining liquid ejection performance by preventing ink 16 supplied from an ink tank 1 from thickening in a print head 10 for ejecting the ink 16 from an ink ejection nozzle formed in the nozzle surface, the ink 16 is heated indirectly by means of heaters 4 and 4 provided on the outside of the ink tank 1 when the temperature of the ink 16 contained in the ink tank 1 lowers below a specified level. Since the ink 16 contained in the ink tank 1 for supplying ink into a print head 3 is prevented from thickening due to temperature drop, ink ejection performance can be sustained.