The present invention provides a method for producing a virus vector, which comprises a step wherein cells that are capable of producing a virus vector are cultured in a culture medium that contains, as active components, a retinoic acid and a histone deacetylase inhibiting substance; and a culture medium for the production of a virus vector, which is characterized by containing, as active components, a retinoic acid and a histone deacetylase inhibiting substance.