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)