Abstract: A cell sorting device using an inexpensive chip capable of being exchanged for each sample. The chip includes: a first flow path allowing buffer fluid containing cells to flow down; second and third flow paths which put the first flow path therebetween and allow buffer fluid not containing cells to flow down; a fourth flow path which allows the buffer fluid as a single flow path formed by joining the buffer fluids in the other three flow paths; a cell detecting region for detecting cells flowing with the buffer fluid down the fourth flow path; and a cell sorting region for sorting the cells according to a type of the cells detected. The first to fourth flow paths are cascaded, are supplied with the buffer fluid from reservoirs with the same fluid level, and have substantially the same width or cross-section area.