PURPOSE: To improve the performance of a picture processing system by transmitting the information of a higher rank like a command having a small quantity of data via an exclusive 2-port memory and processing and transferring the information of a lower rank like the picture data having a large quantity of data via a common memory which is switched by a bus switch circuit.

CONSTITUTION: The information of a higher rank like a command having a small quantity of data is transferred between a CPU 3 of a host computer part 1 and a picture processor 7 of a picture processing circuit part 2 via an exclusive 2-port memory 10. While the information of a lower rank like the picture data is transferred via a common memory 14 which is switched by a bus switch control circuit 12. Thus the data written into a picture memory 8 by the processor 7 can also be written to the memory 14 at one time. As a result, the effective communication is performed between the CPU 3 and the processor 7 without using any large circuit scale.