A radio communication system comprising: a base station device (1, 3); and a plurality of mobile station devices (2, 4) each configured to perform radio communication with the base station device (1, 3), wherein each of the plurality of mobile station devices (2, 4) comprises: a receiver configured to receive from the base station device (1, 3), information indicative of a preamble number of a dedicated preamble assigned by the base station device (1, 3), the dedicated preamble being used for the mobile station device to perform non-contention based random access, and information indicative of an assignment period (T A) of the dedicated preamble, the assignment period indicating a time period for which the dedicated preamble is valid; a transmitter configured to transmit, to the base station device, the dedicated preamble corresponding to the preamble number, on one of a plurality of random access channels; and an upper layer processor (39, 45) configured to, in a case that a random access response to the transmitted dedicated preamble is not received within a time window, control the transmitter to retransmit the dedicated preamble on another one of the plurality of random access channels after the time window has expired and before the assignment period expires, wherein the time window is used for monitoring the random access response, the time window is shorter than the assignment period, the plurality of random access channels are allocated by the base station device to a single carrier, the plurality of random access channels are allocated in frequency domain uniquely for each of the plurality of mobile station devices, and the plurality of random access channels are allocated at a predetermined frame interval in time domain. a base station device (1, 3); and a plurality of mobile station devices (2, 4) each configured to perform radio communication with the base station device (1, 3), wherein each of the plurality of mobile station devices (2, 4) comprises: a receiver configured to receive from the base station device (1, 3), information indicative of a preamble number of a dedicated preamble assigned by the base station device (1, 3), the dedicated preamble being used for the mobile station device to perform non-contention based random access, and information indicative of an assignment period (T A) of the dedicated preamble, the assignment period indicating a time period for which the dedicated preamble is valid; a transmitter configured to transmit, to the base station device, the dedicated preamble corresponding to the preamble number, on one of a plurality of random access channels; and an upper layer processor (39, 45) configured to, in a case that a random access response to the transmitted dedicated preamble is not received within a time window, control the transmitter to retransmit the dedicated preamble on another one of the plurality of random access channels after the time window has expired and before the assignment period expires, wherein a receiver configured to receive from the base station device (1, 3), information indicative of a preamble number of a dedicated preamble assigned by the base station device (1, 3), the dedicated preamble being used for the mobile station device to perform non-contention based random access, and information indicative of an assignment period (T A) of the dedicated preamble, the assignment period indicating a time period for which the dedicated preamble is valid; a transmitter configured to transmit, to the base station device, the dedicated preamble corresponding to the preamble number, on one of a plurality of random access channels; and an upper layer processor (39, 45) configured to, in a case that a random access response to the transmitted dedicated preamble is not received within a time window, control the transmitter to retransmit the dedicated preamble on another one of the plurality of random access channels after the time window has expired and before the assignment period expires, wherein the time window is used for monitoring the random access response, the time window is shorter than the assignment period, the plurality of random access channels are allocated by the base station device to a single carrier, the plurality of random access channels are allocated in frequency domain uniquely for each of the plurality of mobile station devices, and the plurality of random access channels are allocated at a predetermined frame interval in time domain.