Provided are a mobile communication system and a mobile communication method in which a base station apparatus and a mobile station apparatus can efficiently transmit control information in case of communication is conducted by using a wide frequency band constructed by a plurality of component carriers. The mobile communication system in which the base station apparatus and the mobile station apparatus communicate by using the plurality of component carriers, wherein the base station apparatus allocates resources to the mobile station apparatus for transmitting HARQ control information, and the mobile station apparatus uses the allocated resources to transmit to the base station apparatus the HARQ control information for a physical downlink control channel and/or a physical downlink shared channel which are transmitted on a plurality of downlink component carriers, and also a scheduling request for requesting the allocation of uplink data transmission.