The present invention relates to a gene expression regulating sequence consisting of a combination of HRE, E2F and TERT, and to a gene delivery system having significantly improved selective tumor cell cytotoxicity using same, and more particularly, to a recombinant adenovirus. In addition, the present invention relates to a pharmaceutical antitumor composition comprising the recombinant adenovirus. The replication of the recombinant adenovirus of the present invention is tumor-specifically regulated by the novel gene expression regulating sequence of the present invention, thus enabling the recombinant adenovirus of the present invention to exhibit improved selective tumor cell cytotoxicity or apoptotic potential, and exhibit remarkably improved antitumor effects particularly in hypoxic conditions. In addition, the specific expression of the recombinant adenovirus in tumor cells may increase in vivo stability, and thus may induce greatly improved antitumor effects.
