A single-stranded nucleic acid molecule comprising an expression inhibitory sequence that inhibits expression of a target gene, wherein: - the molecule comprises: a region (Xc); a linker region (Lx), an inner region which comprises the expression inhibitory sequence and which is composed of a region and a region, a linker region (Ly) and a region (Yc) in this order; - the region (Xc) is complementary to the region; - the region (Yc) is complementary to the region; and - the linker region (Lx) is represented by the following formula: where: X 1 and X 2 are each independently H 2, O, S, or NH; Y 1 and Y 2 are each independently a single bond, CH 2, NH, O, or S; R 3 is a hydrogen atom or substituent that is bound to C-3, C-4, C-5, or C-6 on a ring A; L 1 is an alkylene chain composed of n atoms, and a hydrogen atom on an alkylene carbon atom may or may not be substituted with OH, OR a, NH 2, NHR a, NR a R b, SH, or SR a, or L 1 is a polyether chain obtained by substituting at least one carbon atom on the alkylene chain with an oxygen atom, provided that: when Y 1 is NH, O, or S, an atom bound to Y 1 in L 1 is carbon, an atom bound to OR 1 in L 1 is carbon, and oxygen atoms are not adjacent to each other; L 2 is an alkylene chain composed of m atoms, and a hydrogen atom on an alkylene carbon atom may or may not be substituted with OH, OR c, NH 2, NHR c, NR c R d, SH, or SR c, or L 2 is a polyether chain obtained by substituting at least one carbon atom on the alkylene chain with an oxygen atom, provided that: when Y 2 is NH, O, or S, an atom bound to Y 2 in L 2 is carbon, an atom bound to OR 2 in L 2 is carbon, and oxygen atoms are not adjacent to each other; R a R b, R c, and R d are each independently a substituent or a protecting group; l is 1 or 2; m is an integer in the range from 0 to 30; n is an integer in the range from 0 to 30; the regions (Xc) and are each linked to the linker region (Lx) via -OR 1 - or -OR 2 -; and R 1 and R 2 may or may not be present, and when they are present, R 1 and R 2 are each independently a nucleotide residue or the structure of the formula. - the molecule comprises: a region (Xc); a linker region (Lx), an inner region which comprises the expression inhibitory sequence and which is composed of a region and a region, a linker region (Ly) and a region (Yc) in this order; - the region (Xc) is complementary to the region; - the region (Yc) is complementary to the region; and - the linker region (Lx) X 1 and X 2 are each independently H 2, O, S, or NH; Y 1 and Y 2 are each independently a single bond, CH 2, NH, O, or S; R 3 is a hydrogen atom or substituent that is bound to C-3, C-4, C-5, or C-6 on a ring A; L 1 is an alkylene chain composed of n atoms, and a hydrogen atom on an alkylene carbon atom may or may not be substituted with OH, OR a, NH 2, NHR a, NR a R b, SH, or SR a, or L 1 is a polyether chain obtained by substituting at least one carbon atom on the alkylene chain with an oxygen atom, provided that: when Y 1 is NH, O, or S, an atom bound to Y 1 in L 1 is carbon, an atom bound to OR 1 in L 1 is carbon, and oxygen atoms are not adjacent to each other; L 2 is an alkylene chain composed of m atoms, and a hydrogen atom on an alkylene carbon atom may or may not be substituted with OH, OR c, NH 2, NHR c, NR c R d, SH, or SR c, or L 2 is a polyether chain obtained by substituting at least one carbon atom on the alkylene chain with an oxygen atom, provided that: when Y 2 is NH, O, or S, an atom bound to Y 2 in L 2 is carbon, an atom bound to OR 2 in L 2 is carbon, and oxygen atoms are not adjacent to each other; R a R b, R c, and R d are each independently a substituent or a protecting group; l is 1 or 2; m is an integer in the range from 0 to 30; n is an integer in the range from 0 to 30; the regions (Xc) and are each linked to the linker region (Lx) via -OR 1 - or -OR 2 -; and R 1 and R 2 may or may not be present, and when they are present, R 1 and R 2 are each independently a nucleotide residue or the structure of the formula.