To provide an emulsifier for cosmetic use which not only has an improved emulsifying power and feel during use, but wherein the emulsifier itself has a skin cell growth-promoting property. The emulsifier contains an aqueous solution of silk protein composed mainly of amorphous silk fibroin, wherein the aqueous solution of silk protein composed mainly of amorphous silk fibroin is an aqueous solution of silk protein obtained by dissolving unscoured, partially scoured or scoured spun silkworm fibers (cocoon filaments) with a neutral salt and then dialyzing the solution.