Abstract: A cell sorter including a well that has a microspace filled with a liquid and having a typical length of 1 mm or less, and that has a bottom surface made of a light-permeable material allowing optical observation of an interior of the microspace; a matrix provided on the bottom surface in the well; a bone fragment placed on the matrix in the well; and osteoclasts placed between the matrix and the bone fragment.

Abstract: A well has a pair of side surfaces, and one of the side surfaces is in contact with a compartment of a first channel with a gas-permeable membrane being interposed therebetween and the other side surface is in contact with a compartment of a second channel with a gas-permeable membrane being interposed therebetween. The well is filled with a liquid cell culture medium, and in such a state, a high-concentration gas and a low-concentration gas, which are different in the concentration of a specific component from each other, are allowed to flow through the first and second channels, respectively, to form a concentration distribution of the specific component in the well.