A method for using a cell culture kit for cultivating cells in a closed system, wherein, the cell culture kit is provided with at least one or more of each of: a culture container for cultivating cells; a culture medium storage container for storing a culture medium or the like; a cell injection container; and a cell collecting container for collecting a suspension of cells after cultivation;- characterized in that: the culture medium storage container is also used as a waste liquid container for collecting a culture medium after cultivation, the culture medium storage container is connected to the culture container through a culture medium storage container connecting tube; the cell injection container is connected to the culture medium storage container connecting tube through a cell injection container connecting tube and the cell collecting container is connected to the culture medium storage container connecting tube through a cell collecting container connecting tube; the cell injection container is connected to a position as close as possible to the culture container in the culture medium storage container connecting tube; the culture medium is transferred from the culture medium storage container to the cell injection container through the culture medium storage container connecting tube and the cell injection container connecting tube and, at this time, air present in the inside of the-the culture medium storage container connecting tube and the cell injection container connecting tube between the culture medium storage container and the cell injection container is moved to the inside of the cell injection container, the cells and the culture medium are transferred from the cell injection container to the culture container while minimizing entrance of air in the culture medium storage connecting tube to the culture container, and the culture medium is transferred from the culture medium storage container to the culture container. a culture container for cultivating cells; a culture medium storage container for storing a culture medium or the like; a cell injection container; and a cell collecting container for collecting a suspension of cells after cultivation;- characterized in that: the culture medium storage container is also used as a waste liquid container for collecting a culture medium after cultivation, the culture medium storage container is connected to the culture container through a culture medium storage container connecting tube; the cell injection container is connected to the culture medium storage container connecting tube through a cell injection container connecting tube and the cell collecting container is connected to the culture medium storage container connecting tube through a cell collecting container connecting tube; the cell injection container is connected to a position as close as possible to the culture container in the culture medium storage container connecting tube; the culture medium is transferred from the culture medium storage container to the cell injection container through the culture medium storage container connecting tube and the cell injection container connecting tube and, at this time, air present in the inside of the-the culture medium storage container connecting tube and the cell injection container connecting tube between the culture medium storage container and the cell injection container is moved to the inside of the cell injection container, the cells and the culture medium are transferred from the cell injection container to the culture container while minimizing entrance of air in the culture medium storage connecting tube to the culture container, and the culture medium is transferred from the culture medium storage container to the culture container. the culture medium storage container is also used as a waste liquid container for collecting a culture medium after cultivation, the culture medium storage container is connected to the culture container through a culture medium storage container connecting tube; the cell injection container is connected to the culture medium storage container connecting tube through a cell injection container connecting tube and the cell collecting container is connected to the culture medium storage container connecting tube through a cell collecting container connecting tube; the cell injection container is connected to a position as close as possible to the culture container in the culture medium storage container connecting tube; the culture medium is transferred from the culture medium storage container to the cell injection container through the culture medium storage container connecting tube and the cell injection container connecting tube and, at this time, air present in the inside of the-the culture medium storage container connecting tube and the cell injection container connecting tube between the culture medium storage container and the cell injection container is moved to the inside of the cell injection container, the cells and the culture medium are transferred from the cell injection container to the culture container while minimizing entrance of air in the culture medium storage connecting tube to the culture container, and the culture medium is transferred from the culture medium storage container to the culture container.