An expression vector characterized by containing an expression unit containing a first selection marker gene and another expression unit containing a second selection marker gene which is different from the above-described first selection marker gene; a transformant having this expression vector; a method of screening cells with the high expression of a recombinant protein with the use of this transformant; and the like. Thus, an expression vector which makes it possible to efficiently screen a recombinant capable of highly expressing a target protein (in particular, a strain capable of highly producing cultured animal cells) at a high reproducibility can be provided.