Provided is a novel nucleic acid molecule that can be produced easily and efficiently and can inhibit the expression of a gene. 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: a region (X); a linker region (Lx); and a region (Xc). The linker region (Lx) is linked between the regions (Xc) and (Xc). The region (Xc) is complementary to the region (X). At least one of the regions (X) and (Xc) includes the expression inhibitory sequence. The linker region (Lx) has a non-nucleotide structure including at least one of a pyrrolidine skeleton and a piperidine skeleton. According to this single-stranded nucleic acid molecule, it is possible to inhibit the expression of the target gene.