PURPOSE: To make a position for setting an original on a contact glass by displaying the original setting extent corresponding to the size of a paper which is fed to an image forming part by the positive column of a neon tube in a flat state.
CONSTITUTION: The neon tubes 4 and 5 having the positive columns whose length from one end side of the tube obtained by glow discharging can be deformed are respectively installed along two neighboring sides of the contact glass 2. That means, the original setting extent display device 3 is installed along the two neighboring sides of the contact glass 2. And in accordance with the selected size of the paper fed to the image forming part, the setting extent for the original G corresponding to the paper on the contact glass 2 is displayed by showing the length of the positive colomns of the neon tubes 4 and 5. Thus, the position on the contact glass 2 where the original G should be set 2 can be made clear, so that erroneous copying can be prevented.