A method for producing a primer supplied to a PCR reaction, the method comprising: a primer designing step of defining a 5'-end-side base sequence of the primer so as to include a base sequence or its complementary base sequence, the base sequence enabling identification of, among thermal cycles in the PCR reaction, a synthesis cycle of a DNA molecule in an amplification product obtained by the PCR reaction performed with the primer, the identification being based on base-sequence data obtained by sequencing the amplification product, and a primer producing step of synthesizing the primer designed in the primer designing step, wherein, in the primer designing step, the primer is a primer used in N-th and N+1-th thermal cycles, N represents an odd number of 1 or more, when N = 1, the step includes defining a complementary DNA fragment constituted by a base sequence that complementarily binds to a 3' end side of an amplification target region in amplification target DNA; defining a non-complementary DNA fragment constituted by a base sequence that does not complementarily bind to the amplification target region; and coupling the non-complementary DNA fragment to a 5' end of the complementary DNA fragment; and when N ≥ 3, the step includes defining a complementary DNA fragment constituted by a base sequence of a non-complementary DNA fragment of a primer used in an N-2-th thermal cycle; defining a non-complementary DNA fragment constituted by a base sequence that is different from each one of base sequences of non-complementary DNA fragments of primers used in 1st to N-2-th thermal cycles, and that does not complementarily bind to the amplification target region; and coupling the non-complementary DNA fragment to a 5' end of the complementary DNA fragment. a primer designing step of defining a 5'-end-side base sequence of the primer so as to include a base sequence or its complementary base sequence, the base sequence enabling identification of, among thermal cycles in the PCR reaction, a synthesis cycle of a DNA molecule in an amplification product obtained by the PCR reaction performed with the primer, the identification being based on base-sequence data obtained by sequencing the amplification product, and a primer producing step of synthesizing the primer designed in the primer designing step, wherein, in the primer designing step, the primer is a primer used in N-th and N+1-th thermal cycles, N represents an odd number of 1 or more, when N = 1, the step includes defining a complementary DNA fragment constituted by a base sequence that complementarily binds to a 3' end side of an amplification target region in amplification target DNA; defining a non-complementary DNA fragment constituted by a base sequence that does not complementarily bind to the amplification target region; and coupling the non-complementary DNA fragment to a 5' end of the complementary DNA fragment; and when N ≥ 3, the step includes defining a complementary DNA fragment constituted by a base sequence of a non-complementary DNA fragment of a primer used in an N-2-th thermal cycle; defining a non-complementary DNA fragment constituted by a base sequence that is different from each one of base sequences of non-complementary DNA fragments of primers used in 1st to N-2-th thermal cycles, and that does not complementarily bind to the amplification target region; and coupling the non-complementary DNA fragment to a 5' end of the complementary DNA fragment. <EOS>