Disclosed is the hardware construction of a radio communication apparatus that can meet advanced radio communications. A control bus for transferring control signals between a main processor and components is separated from a data bus for transferring transmission/receive signals between processor units including sub-processors and an external interface. The sub-processors constitute the processor units, and a software defined radio of the present invention may include plural processor units. The processor units are connected by a dedicated interunit interface. The processor units may include multiple sub-processors, which are connected serially through an interprocessor interface.