A method is disclosed of producing a cell population with a high target cell purity, including changing a character of contaminating cells in a cell population including target cells and the contaminating cells, and removing the contaminating cells and/or collecting the target cells based on the changed character. The disclosure also relates to a cell population with a high target cell purity, produced by the method, and a method of producing a sheet-shaped cell culture, including culturing the cell population into a sheet shape, a sheet-shaped cell culture containing the cell population, a medical composition containing an effective component selected from the group including the cell population and the sheet-shaped cell culture, and a method of treating a disease in a subject, including administering an effective amount of the cell population, the sheet-shaped cell culture or the medical composition, to the subject needing the same.