A conventional shuttle vector constructed by fusing an E. coli-derived plasmid and a transformant-derived plasmid functions in both E. coli and the transformant bacterium, and there exists no expression vector that functions only in a non-E. coli transformant. The present invention provides an plasmid expression vector comprising (1) a plasmid replication unit that functions in an anaerobic microorganism other than E. coli and (2) a protein expression unit formed from DNA coding for a protein having target activity and a DNA fragment containing a promoter and a terminator that function in the anaerobic microorganism. The expression vector of the present invention is capable of being replicated only in a transformant, eliminating the risk of the replication of the transformant gene in other pathogenic or aerobic bacterium, providing an extremely safe and reliable vector and gene transporter for therapeutic application.