Copolymer of hydroxystyrene monomer and (meth) acrylate monomer, and method for producing same

[Problem] To provide a method for producing a copolymer of a hydroxystyrene-based monomer and a (meth) acrylic acid ester-based monomer, whereby the uniformity of the composition ratio and the yield of the copolymer can be improved. [Solution] The present invention is a method for producing a copolymer in which at least one type of hydroxystyrene monomer and at least one type of (meth) acrylic acid ester monomer are polymerized in the presence of a radical polymerization initiator and a solvent, the hydroxystyrene monomer is a hydroxystyrene having a hydroxyl group number of 1-3, or a derivative obtained by protecting at least some of the hydroxyl groups of the hydroxystyrene with a group that is dissociated under the action of an acid or a base. The polymerization reaction is carried out while averaging the consumption rate difference between the monomers under the conditions (1)-(4) described below. (1) A plurality of monomer solutions containing the hydroxystyrene monomer and the (meth) acrylic acid ester