Provided is a nucleic acid complex that comprises a sense chain and an antisense chain, and contains a ligand and a double-stranded nucleic acid containing a double-stranded region having at least 11 base pairs, wherein an oligonucleotide chain that is in the antisense chain and has a chain length of 17-30 nucleotides is complementary to a target [beta]2GPI mRNA sequence, and the 3'-end or the 5'-end of the sense chain has a ligand represented by formula (I), formula (II), formula (III), formula (IV), or formula (V).本發明提供一種核酸複合體等，其係包含正義鏈及反義鏈且含有包含至少11個鹼基對之雙鏈區域之雙鏈核酸與配位子部者，並且該反義鏈中之17個~30個核苷酸之鏈長之寡核苷酸鏈與靶β2GPI mRNA序列互補，於該正義鏈之3'末端或5'末端具有以下之式(I)、式(II)、式(III)、式(IV)或式(V)所表示之配位子部。□
