1. An apparatus for providing a context-aware service, the apparatus comprising: a context-aware service object (CAS) management module which manages CAS information of a CAS and a context which is defined by the CAS; a sensor management module which manages sensor information of a sensor and requests the sensor to observe knowledge; and a context management module which informs the CAS management module of a CAS which defines a context which is provided by the CAS management module when knowledge which is observed satisfies the context which is defined by the CAS, wherein the CAS management module requests the CAS to provide a service if the CAS management module is informed of the CAS by the context management module.