To provide a target nucleic acid measuring method that accurately determines a value showing an initial template amount by using a theoretical expression to which an amount equivalent to an amplification amount of measured nucleic acid is fitted as it is and which accurately reflects an actual PCR amplification efficiency, a target nucleic acid measuring apparatus, a target nucleic acid measuring system, and a target nucleic acid measuring program.

In the target nucleic acid measuring method that calculates an amount equivalent to an initial template amount in a test sample by fitting the number of thermal cycles in a nucleic acid amplification reaction and an amount equivalent to an amplification amount of target nucleic acid measured for each thermal cycle number to the theoretical expression and converts the amount equivalent to the initial template amount to a value showing the initial template amount, the theoretical expression includes an environmental coefficient as an exponent parameter and the amount equivalent to the initial template amount, and includes at least one parameter among amount equivalents to a saturation amount upon the target nucleic acid amplification, a reaction acceleration coefficient, and a reaction inhibition coefficient.