PROBLEM TO BE SOLVED: To provide an inorganic composite powder covered with polymer to improve water dispersibility.SOLUTION: A resin for surface treatment is obtained by copolymerizing a monomer composition containing: at least one monomer (A) selected from acrylamide, dimethylacrylamide, diethylacrylamide, and acryloylmorpholine; and a monomer (B) represented by the following general formula (1) (where, Rrepresents an alkyl group with carbon number 2 or less, Rrepresents an alkyl group with carbon number 2 or less, Rrepresents H or a methyl group, and n is 2 or 3).