Print data is input from a computer, and a main translator of an image processing apparatus analyzes the print data, and performs an output data process. In addition, a sub-translator analyzes the print data, performs an external reference data obtaining process through a network, holds the obtained external reference data in a storage device, and manages the data in a resource management table. When the main translator requires the external reference data, it performs the output data process using the external reference data managed in the resource management table. Thus, the output data process and the external resource pre-reading process are simultaneously performed, thereby improving the throughput of the entire system.