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 C, while a base adjacent with one base spaced apart is A.According to the present invention, the 3' end base is designed to be the base corresponding to SNP; the second and the third bases from the 3' end to be 5'-AT-3', 5'-GT-3', 5'-CA-3' or 5'-CT-3'; and the base sequence of from the fourth from the 3' end to the 5' end base to be completely complementary to the sequence of from a base three bases away from the target SNP base on the 3' side to a desired base.