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 R 1 and R 2 each independently represent a hydrogen atom, a lower alkyl group, or a lower alkoxycarbonyl group; one of R 3 , R 4 , and R 5 represents -O-L 7 -(Xaa) m -L 6 -N 3 , and the remaining two each independently represent a hydrogen atom, a lower alkyl group, or a lower alkoxycarbonyl group; X represents a reactive group; L 6 and L 7 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.