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The problem is to produce iPS cells under serum-free culture conditions without using feeder cells, and to provide a culture method capable of maintaining the undifferentiated state and pluripotent differentiation ability of iPS cells and other such stem cells over an extended period of time under serum-free culture conditions without using feeder cells. The present invention provides: a method for producing induced pluripotent stem cells (iPS cells), characterized in that iPS cells are induced by culturing reprogrammed somatic cells in serum-free medium without using feeder cells, preferably using fibronectin as an adhesion factor; and a method for maintaining the undifferentiated state and pluripotent differentiation ability of stem cells, characterized in that a protein belonging to the tumor growth factor-β (TGF-β) family is added and stem cells are subcultured in serum-free medium without using feeder cells.