The invention provides a method for detection of mutant-type DNA or/and wild-type DNA by contacting at least one of a single-stranded DNA having a substituted nucleotide, a deficient nucleotide region, or an inserted nucleotide region (mutant-type DNA), or/and a wild-type single-stranded DNA corresponding to the mutant-type DNA (wild-type DNA) with a probe hybridizing with both single-stranded DNAs, to form a hybrid with the mutant-type DNA (mutant-type hybrid) or/and a hybrid with the wild-type DNA (wild-type hybrid) (at least one of the obtained mutant-type hybrid and wild-type hybrid has a loop structure), (2) contacting the obtained mutant-type hybrid or/and wild-type hybrid with an intercalator, and (3) detecting the presence or absence of the mutant-type DNA or/and the wild-type DNA by separating the conjugate of mutant-type hybrid and intercalator or/and the conjugate of wild-type hybrid and intercalator.