PURPOSE: To eliminate a background with a threshold level in response to each background density by setting a density area and a threshold level relating to each other, selecting the threshold level through the detection of the density area and using the threshold level so as to eliminate the background.

CONSTITUTION: A threshold level 1 consists of plural threshold levels of representative background density, and a density area detection means 2 detects a background density of an input picture data through the comparison with each of the threshold levels 1. A threshold level decision means 3 selects an applied threshold level for background elimination processing and a background elimination means 4 discriminates whether or not the input picture data is larger than the applied threshold level and discriminates it to be a background when smaller and makes the input picture data zero, and decreases the picture a little for an area in slight excess of the applied threshold level when larger and outputs the input picture data while the data at a high density is kept the same. Thus, even when plural background densities exist like a patched original, the representative background density is detected at each area and the background is eliminated at an optimum threshold level.