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.