Provided are a communication system, a base station apparatus, a mobile station apparatus, and a communication method for reducing interference between uncoordinated adjacent cells. The communication system of the present invention comprises a base station apparatus and a mobile station apparatus. The base station apparatus notifies the mobile station apparatus of a downlink control information format, the downlink control information format including resource allocation information that dictates switching of resource allocation of an uplink demodulation reference signal localized resource allocation and distributed resource allocation, and a frequency offset of the distributed resource allocation of the uplink demodulation reference signal specific to the mobile station apparatus. The mobile station apparatus determines the resource allocation of the uplink demodulation reference signal in accordance with the frequency offset of the mobile station apparatus when information comprised in the downlink control information format dictates the distributed resource allocation in the resource allocation information, and transmits the uplink demodulation reference signal to the base station apparatus.