The present inventors succeeded in cloning the CDT genes of C. coli and C. fetus, which were previously unknown, and in determining their sequences. In addition, the inventors also developed specific primers and primers common to the two species by comparing the CDTs of C. jejuni and C. fetus. Furthermore, the inventors demonstrated that these primers were applicable to multiplex PCR that simultaneously allows for the rapid and convenient determination of the presence of Campylobacter CDT and identification of species, and that they can also be used in PCR-RFLP-based typing.