A novel technique for a simple, rapid, and reliable quantitative analysis of specific DNA sequences was developed. The technique uses an alternately binding quenching probe that binds to either the gene of interest (target) or an internal standard (competitor), in combination with loop-mediated isothermal amplification (LAMP). The difference in quenching abilities of target and competitor DNAs leads to quantitative analysis and the technique was named alternately binding quenching probe competitive LAMP (ABC-LAMP). We quantified amoA gene, as a model target, by ABC-LAMP and real-time PCR. The accuracy of ABC-LAMP was similar to that of real-time PCR. ABC-LAMP also enables the accurate measurement of the gene in the presence of DNA amplification inhibitors such as humic acid and urea which lower the values measured by real-time PCR.