Disclosed is a novel nucleic acid molecule capable of suppressing expression of a gene and capable of easy and efficient manufacture. The single-strand nucleic acid molecule contains an expression suppression sequence that inhibits expression of a target gene, and contains, in order from the 5' end to the 3' end, a 5' end region (Xc), an inner region (Z) and a 3' end region (Yc), wherein the inner region (Z) is constituted by linking an inner 5' end region (X) and an inner 3' end region (Y), the 5' end region (Xc) is complementary to the inner 5' end region (X), the 3' end region (Yc) is complementary to the inner 3' end region (Y), and at least one of the inner region (Z), the 5' end region and the 3' end region includes the aforementioned expression suppression sequence. By means of this single-strand nucleic acid molecule, expression of the target gene can be suppressed.
