[Problem to Be Solved] The present invention is to provide a method of culturing a cell, which method safely increases GDNF mRNA expression without introducing a gene with a virus.[Means to Solve the Problem] A method of producing a cultured cell comprising glial cell line-derived neurotrophic factor (GDNF) mRNA, comprising the step of culturing a human skin-derived stem cell in a serum-free medium comprising at least one of SAG, purmorphamine and sonic hedgehog (SHH) protein. The medium may further comprise B-27 supplement, a ROCK inhibitor, EGF and FGF2.