PROBLEM TO BE SOLVED : To find a new substance which can efficiently proliferate a stem cell while an undifferentiated state is maintained and provide the substance as an undifferentiated state maintaining agent or a proliferation promoter of a stem cell, and to provide a wound healing agent which has wound healing effect of skin, can be easily used in skin regenerative medicine or cosmetic field, and is highly safe and inexpensive.SOLUTION : An undifferentiated state maintaining agent or a proliferation promoter of a stem cell, or a wound healing agent contains phytosterol, phytostenone, or a combination thereof as an active ingredient.SELECTED DRAWING : None