An object of the present invention is to provide a halogenated biotin-modified dimer, which is capable of imaging diagnosis or treatment by labeling with a halogen, a biotin-modified dimer having a high affinity for a mutant streptavidin with a low affinity for natural biotin. The present invention provides a compound represented by the following formula (1) or a salt thereof:
wherein the meaning of each symbol is the same as that described in the specification.