This paper describes the design and implementation of a network-adaptive N-screen game system to be used in cloud computing. The system we are considering needs to generate game video in a cloud server and transmit the video to multiple game devices over an in-home wireless network via a home game server. It is difficult to support multiple screens which have different resolutions with a single bitstream of game video. Therefore, we developed a new network-adaptive game-video extraction and transmission method using (1) scalable video coding and (2) Raptor code techniques. The simulation, conducted with real game-video, verified the efficiency of the proposed video streaming system.