Disclosed are a medium for mammalian somatic cells with which mammalian somatic cells can be grown effectively when the mammalian somatic cells are cultured, while reducing the amount of serum to be added to the medium as much as possible or without adding serum thereto, and an additive to constitute the medium. By blending of a ligand for an endothelial cell differentiation gene (Edg) family receptor and a ligand for a serotonin receptor to a medium, somatic cells of mammals can be grown even in cases where the medium does not contain serum at all or contains only a small amount thereof.