In a method for amplifying the specific nucleic acid sequence, a highly specific amplification which has low possibility of non-specific hybridization can be carried out. Highly stable reagents, the activities of which do not decrease in case of supply and storage, are also provided. Thermostable enzymes are used as RNA dependent DNA polymerase, DNA dependent DNA polymerase, DNA dependent RNA polymerase and ribonuclease H, which are required for the amplification system based on replicated RNA. Especially, it is preferable that a thermostable enzyme derived from Thermus thermophilus which has RNA dependent DNA polymerase activity, DNA dependent DNA polymerase activity and ribonuclease H activity, and thermostable DNA dependent RNA polymerase are used together. By this method, inactivation of enzymes are prevented by using thermostable enzymes, and the amplification can be carried out without sequential addition of enzymes.