In this paper we demonstrate a continuous-flow microbial microreactor that immobilizes microbes into microporous carrier. First, bacteria are trapped into 3, 5, 10, 20-μm-diameter pores using positive dielectrophoresis (DEP). After non-immobilized bacteria are flushed, the continuous-flow microreactor generates reaction products when culture media including reactive substrate are supplied. Continuous-flow type reactors facilitate collecting and evaluating reaction products. We used the developed microreactor to characterize microbes belonging to Corynebacterium group by measuring generated lactic acid when glucose was supplied. The amount of lactic acid produced by a single bacterium was deduced and we found Corynebacterium variabile to be most productive among three tested members. The microbial reactor proposed herein is readily applicable to an efficient microbial screening platform.