A mobile communication apparatus for preventing a second communication from interfering with a first communication in a sub-frame, said mobile communication apparatus being operable to perform the first communication via a base station and the second communication directly communicating with a different mobile communication apparatus, wherein the first communication and the second communication are time-division multiplexed by a first communication sub-frame and a second communication sub-frame, said mobile communication apparatus comprising: a communication channel recognition unit adapted to recognize an unused communication sub-frame which does not interfere with any channel used for the first communication within a wireless area of the base station among a plurality of first communication channels allocated for the first communication; a communication channel substitution controller operable to switch a channel used for the second communication to the unused communication sub-frame recognized by the communication channel recognition unit; and a preamble signal reception recognition unit for recognizing, in accordance with reception of a preamble signal transmitted from the base station for allowing the mobile communication apparatus to establish synchronization with the base station, that the base station exists near the mobile communication apparatus, and for informing the communication channel recognition unit of information indicating the recognition of the existence of the base station; wherein, when the communication channel recognition unit receives from the preamble signal reception recognition unit the information indicating the reception of the preamble signal, the communication channel recognition unit transmits to the communication channel substitution control unit switching control information indicating switching of the previously unused communication sub-frame currently used for the second communication to the first communication, and wherein, when the communication channel substitution control unit receives the switching control information, the communication channel substitution control unit switches the previously unused communication sub-frame currently used for the second communication to the first communication, thus stopping the second communication using the previously unused communication sub-frame and preventing the second communication from interfering with the first communication in the previously unused communication sub-frame. a communication channel recognition unit adapted to recognize an unused communication sub-frame which does not interfere with any channel used for the first communication within a wireless area of the base station among a plurality of first communication channels allocated for the first communication; a communication channel substitution controller operable to switch a channel used for the second communication to the unused communication sub-frame recognized by the communication channel recognition unit; and a preamble signal reception recognition unit for recognizing, in accordance with reception of a preamble signal transmitted from the base station for allowing the mobile communication apparatus to establish synchronization with the base station, that the base station exists near the mobile communication apparatus, and for informing the communication channel recognition unit of information indicating the recognition of the existence of the base station; wherein, when the communication channel recognition unit receives from the preamble signal reception recognition unit the information indicating the reception of the preamble signal, the communication channel recognition unit transmits to the communication channel substitution control unit switching control information indicating switching of the previously unused communication sub-frame currently used for the second communication to the first communication, and wherein, when the communication channel substitution control unit receives the switching control information, the communication channel substitution control unit switches the previously unused communication sub-frame currently used for the second communication to the first communication, thus stopping the second communication using the previously unused communication sub-frame and preventing the second communication from interfering with the first communication in the previously unused communication sub-frame.