Provided is a single-stranded nucleic acid capable of inhibiting expression of a target gene having a delivery function. A molecule containing, from the 5'-side to the 3'-side, a 5'-side region (Xc), a linker region (Lx), an inner region (Z), a linker region (Ly) and a 3'-side region (Yc) in this order, wherein the aforementioned inner region (Z) is constituted by linkage of the inner 5'-side region (X) and the inner 3'-side region (Y), the aforementioned 5'-side region (Xc) is complementary to the aforementioned inner 5'-side region (X), the aforementioned 3'-side region (Yc) is complementary to the aforementioned inner 3'-side region (Y), at least one of the aforementioned inner region (Z), the aforementioned 5'-side region (Xc) and the aforementioned 3'-side region (Yc) comprises an expression inhibitory sequence that inhibits expression of a target gene, and at least one selected from the group consisting of the 5'-terminus, the 3'-terminus, the aforementioned linker region (Lx) and the aforementioned linker region (Ly) is bound to a bio-related substance.
