Provided is an expression vector capable of constitutive expression of a foreign gene in a bacterium belonging to the genus Rhodococcus. The vector is a constitutive expression vector for a bacterium belonging to the genus Rhodococcus comprising: DNA comprising a nucleotide sequence of a mutated TipA gene promoter where a mutation is incorporated into a −10 region sequence of a TipA gene promoter, the mutated TipA gene promoter being capable of thiostrepton-independent and constitutive expression of a gene located downstream thereof; a promoter sequence for the constitutive expression of a foreign gene; a ribosome-binding site sequence located downstream of the promoter sequence; and a multiple-cloning site sequence capable of incorporating a foreign gene therein, located downstream of the ribosome-binding site sequence.