This nucleic acid-encapsulating polymer micelle complex is characterized in being formed of: a block copolymer containing an uncharged hydrophilic polymer chain block and a cationic polymer chain block； and two single-stranded DNA molecules comprising mutually complementary base sequences of 1000 or more bases in length, double-stranded DNA of 1000 or more base pairs in length in which at least a part of the double helix structure has dissociated and taken on a single-stranded structure, or one single-stranded DNA molecule of 1000 or more bases in length.
