A method for supplying an N-screen service by a main N-screen device in a broadcast system is provided. The method includes receiving an Application Information Table (AIT) including a screen_type indicating a type of N-screen device in which a broadcast service application will be run from a broadcast service provider, and one of running the broadcast service application based on the screen_type, performing an operation related to running the broadcast service application by considering a connection relationship between the main N-screen device and a sub N-screen device based on the screen_type, and discarding the AIT based on the screen_type.