Disclosed are a culture medium, an additive, and a method for efficiently inducing the differentiation of mammalian somatic stem cells into cells having the characteristics of bone cells under conditions of serum-free or low-serum culture medium. The culture medium for inducing the differentiation of mammalian somatic stem cells into bone cells comprises a basal medium for culturing mammalian cells, an agent for inducing the differentiation of mammalian somatic stem cells into bone cells, a ligand for endothelial cell differentiation gene (Edg) family receptors and selenium, which culture medium is serum-free or contains a low concentration of serum. The method for inducing differentiation from somatic stem cells into bone cells comprises culturing the somatic stem cells that can differentiate into bone cells in the above-described culture medium.