An immunostimulatory oligonucleotide that is represented by the general formula 5'-Gm-GACGATCGTC-Gn-3' or 5'-Gm-CACGATCGTG-Gn-3' (in the formula, m and n are each independently an integer from 1 to 9 and m+n=10) and that comprises any of the following base sequences: GGACGATCGTCGGGGGGGGG (SEQ. ID. NO.: 1), GGGACGATCGTCGGGGGGGG (SEQ. ID. NO.: 2), GGGGACGATCGTCGGGGGGG (SEQ. ID. NO.: 3), GGGGGGGACGATCGTCGGGG (SEQ ID NO: 4), GGGGGGGGACGATCGTCGGG (SEQ. ID. NO.: 5), GGGGGGGGGACGATCGTCGG (SEQ. ID. NO.: 6), GGGGGGGGGGACGATCGTCG (SEQ. ID. NO.: 7), and GGGGGGGGGCACGATCGTGG (SEQ. ID. NO.: 8).