Disclosed are a communication system, a base station apparatus, a mobile station apparatus, and a method for communication, which facilitate efficient administration of information for settings maintained by base station apparatuses and mobile station apparatuses in a system involving a plurality of component carriers. A mobile communications system including the base station apparatus and the mobile station apparatus administers the system information of one or more component carriers possessing select spectrum width from the system spectrum. When a component carrier is added to the mobile station apparatus, the system applies the system information belonging to the component carriers already connected to the system to the component carrier added thereto.