The object of the present invention is to provide a differentiation inhibiting agent which allows culture of a stem cell or an embryonic stem cell in an undifferentiated state without use of any feeder cell, a method for culturing using the same, a cell culture liquid using the same, and a cell prepared by culturing using this differentiation inhibiting agent. The present invention provides a differentiation inhibiting agent which comprises a low molecular weight compound, especially a tetrahydroisoquinoline derivative, as an active ingredient； a method for safely culturing a stem cell in large scale in undifferentiated state in the absence of feeder cell which comprises culturing a stem cell by using a tetrahydroisoquinoline derivative； a culture liquid for stem cells comprising a tetrahydroisoquinoline derivative； and a cell which is obtained by culture using a tetrahydroisoquinoline derivative as a differentiation inhibiting agent.
