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.
