A pharmaceutical composition includes polymer units α and β, each having a hydrophilic polymer chain bound to a cationic polymer chain, and a drug. The polymer units α and β are radially arranged such that the cationic polymer chains are directed inward and the hydrophilic polymer chains are directed outward, thereby forming a micelle with the drug encapsulated in the micelle. The cationic polymer chain of the polymer unit α has a phenylboronic acid group in a side chain, and the cationic polymer chain of the polymer unit β has a phenylboronic acid binding site in a side chain. The phenylboronic acid group and the phenylboronic acid binding site form a cross-linked structure that can dissociate in an acidic environment and/or in the presence of a substance capable of competitive binding.