There is provided a container unit located outside of a liquid ejection apparatus and configured to supply a liquid to the liquid ejection apparatus via a connection path. The container unit includes: a liquid container configured to contain the liquid, the liquid container having a liquid fill port for pouring the liquid into the liquid container; and a bottom cover member attached to the liquid container and configured to form a bottom face that comes into contact with a mounting surface of the container unit in a liquid supply attitude of the liquid container, in which the liquid is supplied to the liquid ejection apparatus. The bottom cover member has a liquid retainer provided on an opposed face to retain the liquid flow into the opposed face, the opposed face being provided on an opposite side to the bottom face and being opposed to the liquid container.