The present invention relates to a novel bacteriophage having an E.-coli-specific bactericidal activity, a composition for the prevention or treatment of infectious diseases caused by Enterotoxigenic E.-coli comprising the bacteriophage as an active ingredient, an antibiotic comprising the bacteriophage as an active ingredient, a feed additive composition comprising the bacteriophage as an active ingredient, a sanitizer or cleaner comprising the bacteriophage as an active ingredient, and a method for treating colibacillosis using the bacteriophage. The novel bacteriophage of the present invention has a specific bactericidal activity against pathogenic E. coli, and excellent acid- and heat-resistance. Therefore, the novel bacteriophage can be used for the prevention or treatment of swine colibacillosis, which is an infectious disease caused by pathogenic E.-coli, and can also be widely used in animal feed additive compositions, sanitizers, and cleaners.