The present invention addresses the problem of providing a proliferation inhibitor which can act on a cancer stem cell exhibiting resistance to existing anti-cancer agent therapy methods through the inhibition of proliferation of the cell or the apoptosis of the cell. A cancer stem cell proliferation inhibitor which contains a retinoid agonist, preferably tamibarotene, as a sole active ingredient or both the retinoid agonist and a rexinoid agonist, preferably bexarotene, as active ingredients, and which can enhance the effects of various anti-cancer agents when used in combination with each of the anti-cancer agents.
