The present invention relates to a method for efficiently synthesizing or amplifying a nucleic acid containing the target nucleic acid sequence. In the process according to the invention, comprises 3 'sequence at the end portion (A) sequence that hybridizes to (Ac' of the target nucleic acid sequence) at the 3 'end portion, than the sequence in the target nucleic acid sequence (A) 5 a primer comprising a 5 'side of the' complementary sequence (Bc) sequence that hybridizes to (B sequences present (B) on the side ') the sequence (Ac)', the sequence (Ac ' the number of bases) and X, the number of bases of the region flanked by the sequence in the target nucleic acid sequence (a) and the sequence (B) and Y, the sequence (Ac ') and the sequence (B' with) certain number of bases intervening sequence between when the Y '(Y' can be a 0), the range of {X- (Y-Y ')} / X is -1.00~1.00 using primers.