The invention provides a liquid storage unit comprising: a case, a liquid storage part for storing a liquid in the case, with which a liquid port communicates; at least one gas accommodation part for accommodating a gas in the case, with which a gas port communicates, wherein the liquid in the liquid storage part is led out through the liquid port by a pressure of a gas introduced from the gas port; an inner case provided in the case having a pair of openings on opposite side faces thereof; and a pair of flexible partitioning members sealing said pair of openings of the inner case respectively, thereby partitioning the liquid storage part therebetween and defining said at least one of the gas accommodation part in cooperation with the case.