NOVELTY - Primer set for detecting or assaying microorganisms in terephthalic acid containing waste water, comprises oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 4, 6 or 8 and oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 5, 7 or 9 for detecting microorganisms having nucleic acid containing 16S rDNA sequence having 98% or more identity with sequence comprising 1449 base pairs (SEQ ID No. 1 or 2) or 687 base pairs (SEQ ID No. 3), given in the specification.    USE - The primer set is useful for detecting or assaying microorganisms in terephthalic acid containing waste water, monitoring the amount of microorganisms and evaluating methane fermentation efficiency of anaerobic methane fermentation microorganism group contained in terephthalic acid containing waste water (all claimed).    ADVANTAGE - The primer set enables precise detection of microorganisms in terephthalic acid containing waste water and the processing condition of waste water. The amount of microorganisms can be controlled optimal condition and methane fermentation can be performed steadily with high efficiency.    DETAILED DESCRIPTION - Primer set for detecting or assaying microorganisms in terephthalic acid containing waste water, comprises (a) oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 4 and oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 5, for detecting microorganisms having nucleic acid containing 16S rDNA sequence having 98% or more identity with sequence comprising 1449 base pairs (SEQ ID No. 1), given in the specification; (b) oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 6 and oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 7, for detecting microorganisms having nucleic acid containing 16S rDNA sequence having 98% or more identity with sequence comprising 1449 base pairs (SEQ ID No. 2), given in the specification; and/or (c) oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 8 and oligonucleotide having base sequence consisting of or essentially the same as SEQ ID No. 9, for detecting microorganisms having nucleic acid containing 16S rDNA sequence having 98% or more identity with sequence comprising 687 base pairs (SEQ ID No. 3), given in the specification. tagacggaccgccactgcta (SEQ ID No. 4), cctcacctagaccccactaa (SEQ ID No. 5), acgaacgagacccttgcatcta (SEQ ID No. 6), caaccctcaatccgaactaaga (SEQ ID No. 7), aggggagcaaaggggatta (SEQ ID No. 8) and gtcagcttggccttcattctac (SEQ ID No. 9). INDEPENDENT CLAIMS are included for the following:    (1) method for monitoring the amount of microorganisms mentioned in (a)-(c), in anaerobic methane fermentation microorganism group, involves performing PCR using the above mentioned primer set and terephthalic acid containing waste water, and measuring the amount of 16S rDNA of the microorganisms; and    (2) method for evaluating methane fermentation efficiency of anaerobic methane fermentation microorganism group contained in terephthalic acid containing waste water, involves performing PCR using the above mentioned primer set, determining the dominant condition in anaerobic methane fermentation microorganism group, and evaluating methane fermentation efficiency by measuring the amount of 16S rDNA of the microorganisms.