Liquid ejection printing apparatus and liquid supply method to be employed in the same

A liquid ejection printing apparatus performing printing by ejecting a liquid toward a printing medium includes a liquid ejection head portion having a liquid ejecting printing head ejecting a liquid and a first tank (2) holding the liquid to be supplied to the head, a second tank (4) holding a liquid to be supplied to the first tank (2) and having an atmosphere communicating opening for introducing an atmospheric air, a third tank (5) receiving the liquid from the first tank (2) and capable of supplying the liquid to the second tank (4), a first liquid supply passage (6) for communicating the first tank (2) and the second tank (4), a second liquid supply passage (8) for communicating the second tank (4) and the third tank (5), a third liquid supply passage (7) for communicating the third tank (5) to the first tank (2), the first tank (2) and the third tank (5) forming an enclosed space excluding a supply passage connected respectively, a pump (50) capable of sucking a gas within the third tank (5) provided in a passage other than the first, second and third supply passages (6, 8, 7) and a first valve (9) provided in the second supply passage (8) for opening and closing the second liquid supply passage (8), and a second valve (10) provided in the third tank (5) for communicating the gas within the third tank (5) to outside.