PURPOSE: To erase easily an unnecessary image by erasing electrification of a range to be erased of an electrostatic latent image on an image forming member on the basis of coordinate values inputted from the external.

CONSTITUTION: Sliders SL3 and SL4 are provided in the breadthwise direction of an original platen 2 and are moved on a slide resistance 22 to obtain signals VC and VD indicating a masking position. Meanwhile, a synchronizing signal S from a scanning reproducing device 17 is converted to a saw tooth wave S1 and is inputted to window comparators 24 and 25 together with signals VC and VD to obtain a pulse signal S2, and this signal is inverted by a transistor Tr1 and is inputted to one input of an AND circuit 26. Outputs of sliders SL1 and SL2 in the Y direction of the original platen 2 are inputted to R and S terminals of an FF27 to obtain an output, and this output is inputted to the other input of the AND circuit 26. When the AND circuit 26 is opened, signals corresponding to positions of sliders SL1WSL4 in X and Y directions are inputted to a control electrode 17a of the scanning reproducing device 17 after passing a video amplifier 28. Thus, electrification of an area ABCA is erased easily.