Provided is a method for advancing nucleic drugs using a complex comprising double-stranded RNA and a nucleic acid binder comprising a cationic oligopeptide. In the present invention: nuclease resistance is exhibited in a "double-stranded RNA-cationic oligopeptide complex" having bonded thereto a cationic oligopeptide having an amino group associated to a side chain thereof； and, at the same time, the double-stranded RNA to be bonded remains highly active. Secondly: the bonding to and heat stability relative to double-stranded nucleic acid is further improved in a cationic oligopeptide having a guanidino group associated to the side chain thereof； bonding to B-type double-stranded nucleic acid being the main state of double-stranded DNA is also possible； and resistance to nuclease in the complex is found. In addition, RNaseH action can be promoted by bonding this cationic oligopeptide to a chimeric double strand such as an RNA-DNA complex double strand, etc.
