The invention provides a copolymer capable of causing hydrophilic-hydrophobic variation at the specific temperature and pH, and a lipidosome compound capable of releasing an inclusion at the specific temperature and pH and prepared via compounding the copolymer. The copolymer has a repetitive unit (a) of a monomer represented by the following general formula (1), a repetitive unit (b) of a monomer containing carboxyl groups, and a repetitive unit (c) of a monomer represented by the following general formula (2). The lipidosome compound is obtained by compounding the copolymer. In the formula (1), R1 represents a hydrogen atom or a methyl group R2 represents an alkyl group having 1-4 carbon atoms and n represents a natural number of 1-4. In the formula (2), R3 represents a hydrogen atom or a methyl group R4 represents an alkyl group having 8-20 carbon atoms or an alkenyl group having 8-20 carbon atoms and m represents a natural number of 1-6.
