The present invention provides a double-stranded polynucleotide having a sense strand polynucleotide consisting of a nucleotide sequence complementary to a target sequence in a target gene, and an antisense strand polynucleotide having a nucleotide sequence complementary to the sense strand polynucleotide, wherein an aryl or heteroaryl compound is bound to a phosphate group at the 5-end of the antisense strand polynucleotide.