The purpose of the present invention is to provide a preparation for preventing or treating type I diabetes, said preparation exerting an excellent effect of preventing or treating type I diabetes, and a method for preventing or treating type I diabetes. The onset and symptoms of type I diabetes can be very remarkably relieved by dosing a combination of: (A) at least one member selected from the group consisting of proinsulin, insulin, insulin A chain, insulin B chain, fragments thereof and variants thereof； with (B) α-GalCer.
