The purpose of the present invention is to provide: a copolymer for cosmetics, which has excellent water repellency and oil repellency even though a polyfluoroalkyl group therein has 6 or less carbon atoms a surface treatment agent which contains the copolymer for cosmetics a powder for cosmetics, which is treated with the surface treatment agent and has excellent water repellency and oil repellency and a cosmetic preparation which contains the powder for cosmetics. A copolymer for cosmetics of the present invention contains: 70-90% by mass of a constituent unit (A) that is derived from a compound represented by formula (a) 2-25% by mass of a constituent unit (B) that is derived from a compound represented by formula (b) 2-25% by mass of a constituent unit (C) that is derived from a compound represented by formula (c) 0.1-10% by mass of a constituent unit (D) that is derived from a compound represented by formula (d) and a residue (E) of a chain-transfer agent (e) that contains an OH group or a COOH group. CH2=CR1-COO-Q1-Rf (a) CH2=CR2-Q2-COOH (b) CH2=CR3-COO-(R4O)n-R5 (c) CH2=CR7-COO-Q3-P(O)(OH)-R8 (d)
