Method for filling liquid into liquid container with liquid chamber, and liquid filling apparatus

A method of supplying liquid into a liquid container, which includes a first chamber, provided with a liquid supply portion for supplying liquid out, to a liquid ejection head and an air vent for fluid communication with ambient air, for accommodating therein a negative pressure producing member; a second chamber forming a substantially sealed space except for a communication part with the first chamber, wherein the liquid supply portion is disposed at a bottom side; and a gas-liquid exchange promoting structure, provided in the first chamber, for introducing the ambient air into the second chamber to permit discharging of the liquid, the method includes a pressure reducing step of reducing a pressure of an entirety of the container, while the liquid container is hermetically sealed; first liquid supplying step of supplying the liquid into the second chamber, and completing the liquid supply before a portion adjacent to the gas-liquid exchange promoting structure of the negative pressure producing member in the first chamber is supplied with the liquid, in a reduced pressure state provided by the pressure reducing step, with the container taking the same orientation as when the liquid supplied to the liquid ejecting head; a second liquid supplying step of supplying the liquid into the first chamber through the liquid supply portion, after the first liquid supplying step into the second chamber; a releasing step of releasing the hermetically sealed state of the first chamber after the second liquid supplying step into the first chamber.