A vector for constitutively expressing a high level of a target protein, and more particularly a RepE mutant protein containing a deletion of 21 amino acids in the C-terminal region of a RepE protein and a vector for constitutively expressing a high level of a target protein, which comprises a gene encoding the mutant protein. The constitutive high-level expression vector can stably express a high level of a target protein. Also, the surface expression vector can express a target protein on the surface of recombinant microorganisms while constitutively expressing a high level of the target protein, and thus will be useful for construction of an antigen for vaccines.