An image processing/communication system provided with a processing unit for performing a coding processing on image data, a plurality of line memories for storing image data related to the coding processing and coding data, an external-bus connection control unit for controlling a connection between the external bus and the system, an internal bus for transferring data to the processing unit, the external-bus connection control unit and the plurality of line memories, and an operation control unit for causing the processing unit, the plurality of line memories and the external-bus connection control unit to simultaneously perform an input operation of inputting image data from the external bus to the line memory and an output operation of outputting coding data to the external bus from the processing unit or the line memory in parallel with one another. Thus, in each operation of this system, a coding processing can be effected by using the line memory. Therefore, an access to an external bus, which is necessary in the conventional system, becomes unnecessary. Moreover, a coding operation, a data input operation of inputting data from and a data output operation of outputting data to the external bus can be performed in parallel with one another. Thus, a coding operation can be performed extremely quickly.