PURPOSE: To enable to reject the information related to the character describing frame without using optical filter.

CONSTITUTION: The analog video element signal having the level corresponding to the concentration of each video element of the document obtained with photo electric scanning is quantized into a plurality of levels from the level 0 to the level 7 with the quantization circuit 10. The level 0 is set at PCS values 0.00W0.05, the quantization is made up to 4 at 0.05 width, the levels 5 and 6 are quantized at 0.25 increment, and the PCS value of 0.75 or more is set at the level 7. The number of the video element signal from the level 0 to the level 2 is counted at the binary counter 14 every vertical scanning, and the count value is sequentially shifted in the shift registers 15W19 every end of each vertical scanning. The result of vertical scanning five times in succession is outputted from the registers 15 to 19, it is compared with the limit value 25 at the comparators 20W24, and when the video element signal is judged as the described frame part, conversion indication is made.