Emulsifying agents of the natural polvymer type, especially polysaccharide type, attain excellent emulsion stability and give a stable emulsion. However, their emulsifying power is not always high and these emulsifying agents have been still insufficient in giving an emulsion having a small particle diameter. A polymer-type emulsifying agent is provided which has high emulsifying power and with which an emulsion having a small emulsified-particle diameter can be obtained. The emulsifying agent, which is of the natural polymer type having high emulsifying power, is an emulsifying agent containing as an active ingredient a composite of a polysaccharide with a specific protein which was contained in soybean and has a proline content of 10% or higher and a molecular weight of 50,000-80,000 Da.