Provided are non-aggregating immunostimulatory oligonucleotides. The present invention also provides a delivery agent for an immunostimulatory-oligonucleotide nucleic acid medicine, said delivery agent including a nucleic acid that contains a phosphorothioated nucleotide. According to another aspect, the present invention further provides an oligonucleotide including a bioactive core, and a nucleic acid that contains a phosphorothioated nucleotide. The present invention yet further provides an immunostimulator including the bioactive core of a type A/D, type B/K, or type C immunostimulatory oligonucleotide.