PURPOSE: To simplify the constitution, to reduce the cost, and also, to execute an arithmetic processing at a high speed and with high use efficiency by using an area in which video data in a video memory is stored, and other remaining area than this area, and executing an operation of an image synthetic processing, etc., between two video data by a single video memory.

CONSTITUTION: In other remaining area B than an area A in which video data in a video memory 1 is stored already, other video data is fetched successively, an operation is executed between its video data and the video data stored already, and a result of operation is stored again in the video memory 1. Also, therefore, this device is provided with a video memory 1 which can execute independently a random access and a serial access, a memory controller 2 for controlling this video memory 1, a video data store means 3 for storing the video data in the video memory 1, and an arithmetic means 4 for executing an operation between the image data stored in the video memory 1.