The present invention aims to provide a nucleic acid molecule having improved stability in serum and capable of exhibiting a gene expression regulation function after transfer into the cell. A cyclic nucleic acid molecule represented by the following formula (A):wherein each symbol is as described in the DESCRIPTION can be synthesized easily at a low cost, and can inhibit the translation of a protein encoded by the gene. Since the cyclic nucleic acid molecule of the present invention can inhibit the expression of a target gene as described above, for example, it is useful as a pharmaceutical product, a diagnostic agent, an agricultural chemical, and a tool for conducting research on agriculture, medical science, life science, and the like.
