Provided are a communication system, a base station device, a mobile station device, and a communication method which can effectively manage measurement information held by a base station device and a mobile station device in a system having a plurality of component carriers. The mobile station device is used in a mobile communication system configured by a base station device and a mobile station device. For a plurality of cells having different frequencies, a reference cell with respect to an object to be measured is defined as a measurement reference cell when executing a measurement. The mobile station device specifies one or more of the measurement reference cell for the object to be measured and executes a measurement of the object to be measured for the specified one or more of the measurement reference cell.
