PURPOSE: To easily recognize a desired picture before inversion without assimilating it to a background even when inverting slight forms (dots, lines, etc.) differed from the background by displaying inversely the desired picture based on invertion correcting information stored in a correcting information storage means.

CONSTITUTION: Picture information obtained by photographing is stored in a picture memory 13, this picture information is transmitted to a window processing means 16 together with the inversion correcting information composed of a characteristic curve G stored in a positive memory 19a by a control singal from a central processing unite 12, and the means 16 adds correcting information to the picture information and executes the window processing. Then the window information is transmitted to a D/A converter 17, the window information is converted by the D/A converter and transmitted to a display means 18. Finally the D/A converted window information is displayed as the desired picture.