A mobile station apparatus determines an uplink carrier component to which a physical downlink control channel instructing to start random access procedure corresponds. A wireless communication system includes a base station apparatus and a mobile station apparatus that communicate with each other using a plurality of component carriers. The base station apparatus includes a random access controller that preliminarily allocates random access resources corresponding to a specific downlink component. A transmission processor transmits control information instructing to start the random access procedure. The mobile station apparatus includes a random access processor that, upon receipt of the control information instructing to start the random access procedure, starts the random access procedure by means of the random access resource corresponding to a specific downlink component carrier preliminarily allocated by the base station apparatus.