Abstract: A vector expressing two foreign genes by using RRE sequence and controlling the ratio of the expression doses of these genes owing to the modification is provided. This vector, which can be provided as a lentivirus vector based on SIVagm, is constructed by modifying a virus-origin expression regulatory sequence into another expression regulatory sequence so as to eliminate the dependency on the virus-origin protein. Although this vector has a packaging signal, it has been modified so that the risk of the occurrence of wild strains due to gene recombination is lowered and no virus structural protein is expressed. This vector is highly useful as a gene therapeutic vector with a need for transferring two genes while controlling the expression doses or expression dose ration thereof.