PURPOSE: To eliminate the lack of data by using the breadth-wise size of a picture data display area and the breadth-wise size of picture data, adding the display causes of an output device to these sizes, calculating a display magnification and calculating the length-wise size of the display area.

CONSTITUTION: Fair copy instructing information 101 instruct the size of the picture data display area only by the number of columns in the breadth-wise direction of the display area. In picture data information 102, there are a picture data length-wise size and a picture data breadth-wise size, which are the number of picture elements in the length-wise and breadth-wise directions of the picture data to be displayed, and the picture data. Then, output device information 103 keep the number of the picture elements in the row and column of the output device and information for enlarging and reducing the picture data. A picture data display area size calculating part 104 calculates the display magnification based on the instructing size of the picture data display area, the breadth-wise size of the picture data and the output device information and calculates the length-wise size of the picture data display area from the display magnification and the length-wise size of the picture data. Thus, there is no part to lack the picture data, for which a length-wise and breadth-wise ratio is 1 to 1, and the picture data can be displayed without any vain space part.