The loop-mediated isothermal amplification (LAMP) is a novel nucleic acid amplification method that uses only one type of enzyme. One of the characteristics of the LAMP method is its ability to synthesize extremely large amount of DNA. Accordingly, a large amount of by-product, pyrophosphate ion, is produced, yielding white precipitate of magnesium pyrophosphate in the reaction mixture. Judging the presence or absence of this white precipitate allows easy distinction of whether nucleic acid was amplified by the LAMP method. Since an increase in the turbidity of the reaction mixture according to the production of precipitate correlates with the amount of DNA synthesized, real-time monitoring of the LAMP reaction was achieved by real-time measurement of turbidity.