A simple and rapid bacteria detection device for on-site evaluation of oral hygiene in hospitals and clinics was demonstrated. The developed device utilizes dielectrophoretic impedance measurement (DEPIM) method. We integrated a micro electrode chip on which bacteria were captured by dielectrophoresis (DEP), an AC voltage source to induce DEP force, and an impedance measurement circuit to a portable instrument that enables rapid and automated oral bacterial inspection in hospitals and clinics. Special considerations have been made on effects of high electrical conductivity of oral samples on DEP force and DEPIM results. It was shown experimentally and theoretically that using a higher electric field frequency for the DEP bacteria trap and the impedance measurement could realize DEPIM application to bacteria inspection from oral samples with higher conductivity. Based on these investigations, we optimized the frequency condition of the DEPIM suitable for inspecting an oral sample along with the design and development of a portable DEPIM apparatus for on-site inspection of oral bacteria.