The present invention provides an emulsifier composed of a core-corona type microparticle whose emulsifying power is not influenced by crosslinking level, and an oil-in-water emulsified cosmetic which is emulsified with the emulsifier.A cosmetic raw material is composed of a core-corona type microparticle, the core-corono type microparticle being obtained by radical polymerization of a polyethylene oxide macromonomer represented by the following formula (1) nad one or more hydrophobic monomers selected from acrylate derivative monomers represented by the formula (2) and acrylamide derivative monomers represented by the following formula (3), under the following conditions (A) to (D) (A) the molar ratio represented by the fed molar amount of the polyethylene oxide macromonomer the fed molar amount of (the acrylate derivative monomer and/or the acrylamide derivative monomer) is 1:10 to 1:250, (B) the macromonomer represented by the following formula (1) is an acrylic acid derivative or a methacrylic acid derivative having a polyethylene glycol group with a repeating unit of 8 to 200, the acrylate derivative monomer represented by the following formula (2) is an acrylic acid derivative or a methacrylic acid derivative having a substituent containing an alkyl group with 1 to 12 carbon atoms, the acrylamide derivative monomer represented by the following formula (3) is an acrylamide derivative or a methacrylamide derivative having a substituent containing an alkyl group with 1 to 18 carbon atoms, (C) the polymerization solvent is a water-alcohol mixed solvent, and the alcohol is one or more selected from ethanol, dipropylene glycol, 1,3-butylene glycol, isoprene glycol, (D) the solvent composition of the water-alcohol mixed solvent is water: alcohol = 90 to 10:10 to 90 by mass ratio at 20℃, R1 represents H or an alkyl group having 1 to 3 carbon atoms, n represents a number of 8 to 200. X represents H or CH3.R2 represents H or an alkyl group having 1 to 3 carbon atom
