The present invention provides a double-strandednucleic acid consisting of a sense-strand nucleic acidand an antisense-strand nucleic acid and comprising adouble-strand region having at least 11 base pairs, forsuppressing expression of APCS gene, in which anoligonucleotide chain having a chain length of at least17 nucleotides and at most 30 nucleotides in theantisense-strand nucleic acid is complementary to atarget APCS mRNA sequence comprising a base sequence setforth in any one of SEQ ID NOS: 1288 to 1930.