Provided is a novel nucleic acid molecule that can inhibit the expression of a gene and can be produces easily and efficiently. The nucleic acid molecule is a single-stranded nucleic acid molecule including an expression inhibitory sequence that inhibits expression of a target gene. The single-stranded nucleic acid molecule includes, in sequence from the 5 side to the 3 side: a 5 side region (Xc) an inner region (Z) and a 3 side region (Yc). The inner region (Z) is composed of an inner 5 side region (X) and an inner 3 side region (Y) that are linked to each other. The 5 side region (Xc) is complementary to the inner 5 side region (X). The 3 side region (Yc) is complementary to the inner 3 side region (Y). At least one of the inner region (Z), the 5 side region (Xc), and the 3 side region (Yc) includes the expression inhibitory sequence. According to this single-stranded nucleic acid molecule, it is possible to inhibit the expression of the target gene.
