An object of the present invention is to provide an allele specific primer which is accompanied by less possibility of the false positive and enables definite discrimination when a base immediately adjacent to on the 3' side of a target SNP base is A, while a base adjacent with one base spaced apart is T.According to the present invention, the 3' end base is designed to be the base corresponding to SNP; the second base from the 3' end to be C; the third base from the 3' end to be any one of T, C or G; and the base sequence of from the fourth from the 3' end to the 5' end base to be complementary to the sequence of from a base three bases away from the target SNP base on the 3' side to a desired base.