Patent ID: 8029115

Claim:
A liquid ejection device comprising: a main tank mounting unit to which a main tank capable of storing liquid is removably mountable; a sub tank comprising: an inlet configured to be brought into fluid communication with the main tank in a state where the main tank is mounted to the main tank mounting unit; and an outlet; an ejection head having a nozzle configured to eject the liquid supplied from the sub tank via the outlet; a remaining amount detecting unit configured to detect whether an amount of the liquid in the main tank is equal to or smaller than a predetermined liquid amount, where a liquid level of the liquid in the main tank at the predetermined liquid amount is positioned at a threshold level; and a remaining amount calculating unit configured to determine a liquid amount ejected from the ejection head during a term starting from a detection of the threshold level by the remaining amount detecting unit, thereby calculating a remaining liquid amount in the main tank; wherein the sub tank is configured to satisfy the following formula: S H −S L ≦M H −M N where, S H is a liquid amount in the sub tank in a balanced state at which the liquid has flowed into the sub tank by a hydraulic head pressure on mounting the main tank with the liquid fully filled; S L is a liquid amount in the sub tank in a state where the liquid level is positioned at the outlet of the sub tank; M H is a liquid amount in the main tank when the liquid is fully filled in the main tank; and M N is a liquid amount in the main tank in a state where the liquid level is positioned at the threshold level, and wherein the main tank mounted to the main tank mounting unit is disposed adjacent to the sub tank in a horizontal direction, and the liquid level in the main tank is equalized to the liquid level in the sub tank by the hydraulic head pressure of the liquid in the main tank and the sub tank when the main tank in a fully filled state is mounted to the main tank mounting unit.