[Problem] The present invention addresses the problem of providing a polymerized prodrug of a nucleic acid antimetabolite, said prodrug having an improved antitumor effect and having few side effects, particularly myelosuppression. In particular, the invention addresses the problem of providing a nucleic acid antimetabolite that exhibits a tumor growth inhibition effect over a long period of time and does not prolong myelosuppression. [Solution] Provided is a multi-branched compound to which a nucleic acid antimetabolite is bonded, said compound being characterized by being appropriately provided, in a terminal functional group of a multi-branched polymer carrier, with a substituent group that includes a plurality of polyethylene glycol segments and succinic acid monoamide units to which a nucleic acid antimetabolite is bonded. The multi-branched compound, when administered inside the body, is retained in the blood and is distributed in the body, the nucleic acid antimetabolite bonded to said compound can be made to act with an appropriate release profile, drug efficacy can be improved, and side effects can be prevented. In particular, the present invention makes it possible to provide a drug that prevents the prolongation of myelosuppression, which is the main side effect of nucleic acid antimetabolites.[Problème] La présente invention aborde le problème consistant à fournir un promédicament polymérisé d'un antimétabolite d'acide nucléique, ledit promédicament possédant un effet antitumoral amélioré et présentant peu d'effets secondaires, en particulier en ce qui concerne la myélosuppression. En particulier, l'invention aborde le problème dconsistant à fournir un antimétabolite d'acide nucléique qui présente un effet inhibiteur sur la croissance tumorale sur une longue période de temps et qui ne prolonge pas la myélosuppression. [Solution] L'invention concerne un composé multi-ramifié sur lequel est lié un antimétabolite d'acide nucléique, ledit composé étant carac
