To prepare high-performance specific gene-amplification primers for detecting, quantitatively determining or identifying Vibrio parahaeinolyticus having low possibility of mis-identification and practically sufficient amplification efficiency and amplification specificity.We have determined the nucleotide sequences of rpoD genes encoding RNA polymerase .sigma.70 factor of type strains of the genus Vibrio and of stock strains of Vibrio parahaemolyticus (strains containing and those not containing toxin gene); elucidated the phylogenetic relation, and identified nucleotides which are characteristic in Vibrio parahaemolyticus, thereby enabling the design of probes containing them and having high specificity, and primers for gene amplification having high specificity and excellent amplification efficiency.