A mobile station apparatus that communicates with a base station apparatus, the mobile station apparatus comprising: a receiving part for receiving a physical downlink control channel and a radio resource control signal including configuration information for an aperiodic sounding signal; and a transmitting part for transmitting the aperiodic sounding reference signal in a case that the physical downlink control channel includes information for indicating transmission of the aperiodic sounding reference signal; wherein the aperiodic sounding reference signal is transmitted until a number of transmissions of the aperiodic sounding reference signal reaches a repetition number, in a case that the configuration information indicates the repetition number; and the aperiodic sounding reference signal is transmitted with frequency hopping until the number of transmissions of the aperiodic sounding reference signal reaches the repetition number, in a second case that the configuration information indicates the repetition number and the frequency hopping; and the aperiodic sounding reference signal is transmitted with antenna switching until the number of transmissions of the aperiodic sounding reference signal reaches the repetition number, in a third case that the configuration information indicates the repetition number and the antenna switching, wherein the aperiodic sounding reference signal is transmitted on a component carrier, in a case that the physical downlink control channel includes information for indicating the component carrier, and the transmission power of the aperiodic sounding reference signal is controlled by a transmission power control command, in a case that the physical downlink control channel includes information for indicating transmission of the aperiodic sounding reference signal and the transmission power control command. a receiving part for receiving a physical downlink control channel and a radio resource control signal including configuration information for an aperiodic sounding signal; and a transmitting part for transmitting the aperiodic sounding reference signal in a case that the physical downlink control channel includes information for indicating transmission of the aperiodic sounding reference signal; wherein the aperiodic sounding reference signal is transmitted until a number of transmissions of the aperiodic sounding reference signal reaches a repetition number, in a case that the configuration information indicates the repetition number; and the aperiodic sounding reference signal is transmitted with frequency hopping until the number of transmissions of the aperiodic sounding reference signal reaches the repetition number, in a second case that the configuration information indicates the repetition number and the frequency hopping; and the aperiodic sounding reference signal is transmitted with antenna switching until the number of transmissions of the aperiodic sounding reference signal reaches the repetition number, in a third case that the configuration information indicates the repetition number and the antenna switching, wherein the aperiodic sounding reference signal is transmitted on a component carrier, in a case that the physical downlink control channel includes information for indicating the component carrier, and the transmission power of the aperiodic sounding reference signal is controlled by a transmission power control command, in a case that the physical downlink control channel includes information for indicating transmission of the aperiodic sounding reference signal and the transmission power control command.