An oxygen scavenger installed in a cap used for liquid substance containing vessel, having an inner structure composed of an upper vacant compartment, which has plural perforations from outside, and a lower container compartment, which contains the oxygen scavenger and is partitioned at two places in a range from said perforations to said lower container compartment by using single or plural sheets of gas permeable liquid proofing sheets to isolate duplicately the oxygen scavenger from the liquid substance, and a cap equipped with said container are represented. The cap is particularly useful for preservation of liquid food and developing solution.