In general, according to one embodiment, a method containing, reverse-transcribing the first sequence in the target RNA, to obtain a reverse-transcription product containing a first' sequence complementary to the first sequence, dissociating the reverse-transcription product from the target RNA, hybridizing an elongation primer and the reverse-transcription product to elongate both, thereby obtain an elongation product, and maintaining the amplification reaction liquid containing the elongation product, a primer set and Tin(exo-) DMA polymerase and/or Bsm DMA polymerase under an amplification reaction condition, to amplify the first' sequence.