Provided are: a polymer compound for efficiently delivering two drugs to an affected area, reducing side effects, and increasing drug efficacy; and an antitumor drug having said polymer compound as an active ingredient. This polymer compound is obtained by ester-bonding a camptothecin derivative and an HSP90 inhibitor to a carboxyl group of a side-chain of a block copolymer obtained by joining a polyethylene glycol segment and a polyglutamic acid segment to one another.