PURPOSE: To heat uniformly all of the surface of an image forming part to prevent moisture absorption, dew condensation, and the degradation in characteristic in a low-temperature environment by winding the image forming part of a belt-shaped image carrier around a take-up roll so that it does not overlap.

CONSTITUTION: A photosensitive body A is a long-sized sheet and has an image forming part A1 corresponding to the size of a display window 2 in the center part and has a front guide sheet A2 and a rear guide sheet A2 before and after this part A1 respectively, and an attaching member 19 is provided in the front end of the front guide sheet A2, and an attaching member 20 is provided in the rear end of the rear guide sheet A2 similarly. The attaching member 19 is fixed to a driving roll 6, and the attaching member 20 is fixed to a take-up roll 5, and the peripheral length of the take-up roll 5 is longer than the image forming part A1. In the initial position, the image forming part A1 is wound around the take-up roll 5 by <1 turn so that the image forming part A1 does not overlap, and the rear guide sheet A3 is wound there by about integer-number of turns, and the thickness of the sheet wound under the image forming part A1 is approximately uniform, and a heater 25 heats effectively all of the surface of the image forming part A1 uniformly.