Enhanced resistance to degradation ability against nucleases nucleic acid fragments of single stranded or double stranded, including a base sequence of the functional nucleic acid in a simple and low cost, it is an object to improve.
On at least one end of the single-stranded nucleic acid fragments or double-stranded nucleic acid fragments, (A) a nucleic acid region consisting of two to five any nucleotide, (B) gna or Gnna (where each n is, independently a, g, t, a, or c, a nucleic acid consisting of the nucleotide analog or a nucleic acid region consisting of the nucleotide sequence of the is) any modified bases, and (C) a nucleotide sequence complementary to the nucleic acid region of the (a) consists regions, they are linked a linked hairpin DNA in order toward 'from the distal side 3' 5 distally.