Abstract: A purpose of the present invention is to provide a small chemical compound which especially promotes induction of the differentiation of ES cells into insulin-producing cells. Another purpose of the present invention is to provide: a method for inducing the differentiation of ES cells into insulin-producing cells using the compound; and an agent for promoting induction of the differentiation into insulin-producing cells. Another purpose of the present invention is to provide the thus-induced insulin-producing cells. Provided are: an agent for promoting induction of the differentiation of stem cells derived from a mammal into insulin-producing cells, which contains a compound that is selected from the group consisting of dopamine metabolism inhibitors, serotonin metabolism inhibitors, acetylchotine, acetylcholine degrading enzyme inhibitors and acetylcholine receptor activators; and a method for inducing differentiation using the agent for promoting induction of differentiation.