PROBLEM TO BE SOLVED: To provide a non-modified oligonucleotide with less in side effects, having high Th1 immune stimulating activity with clinical application possibility.SOLUTION: The immune stimulating oligonucleotide comprises core base sequences represented by a general formula: 5GTCGTT3, and a linkage base sequence composed of one or more bases linking the core base sequences, while containing 4 or more the core base sequences.