Abstract: It is an object of the present invention to provide a conjugate of a duocarmycin derivative and a biotin-modified dimer, which is useful for pretargeting methods. According to the present invention, a compound represented by the following formula (1) or formula (2) is provided: wherein R1 and R2 each independently represent a hydrogen atom, a lower alkyl group, or a lower alkoxycarbonyl group; one of R3, R4, and R5 represents —O-L7-(Xaa)m-L6-N3, and the remaining two each independently represent a hydrogen atom, a lower alkyl group, or a lower alkoxycarbonyl group; X represents a reactive group; L6 and L7 each independently represent a divalent linking group; Xaa represents an amino acid residue; m represents an integer of 2 to 10; and Me represents a methyl group.