Provided are: a radiolabeled drug, which is efficiently accumulated in a target and has high in vivo stability； and diagnosis and treatment each using the radiolabeled drug. Specifically provided are: a radiolabeled drug showing increased accumulation in a target site, which comprises a complex composed of a ligand that is bound to a compound capable of binding to a target molecule and forms a polycoordinated complex with a metal (e.g., technetium or rhenium) and a radionuclide of the metal； the radiolabeled drug for diagnosis or treatment； a ligand for preparing the radiolabeled drug； a kit that comprises a drug comprising the ligand and a drug comprising a radionuclide of a metal, as separate package units； and a method of increasing accumulation of a radiolabeled drug in a target site, comprising using the above-mentioned radiolabeled drug.
