The present invention provides a natural type miRNA, which is a single-stranded nucleic acid containing X region and Y region,wherein the 3'-terminus of said X region and the 5'-terminus of said Y region are linked via a linker region of a non-nucleotide structure,the X region contains (a) a guide strand sequence or (b) a passenger strand sequence of a mature miRNA,when the X region contains (a), the Y region contains a passenger strand sequence of the mature miRNA,when the X region contains (b), the Y region contains a guide strand sequence of the mature miRNA, andthe guide strand sequence and the passenger strand sequence form a double-stranded structure.
