PURPOSE: To prevent the waving of a photosensitive belt from generating and to obtain an excellent quality image by eliminating a gap between a roller and the belt on the central part of the photosensitive belt.

CONSTITUTION: On a photosensitive belt traveling device 11, the photosensitive belt 11a is spread between a first roller 30 and a second roller 31 composed of the elastic body of low hardness. Either of the rollers 30 and 31 is pressed in the direction opposite to the other roller to impart tension to the photosensitive belt 11a. Then, the first/second rollers 30 and 31 have load distributions (w) shown by the figure, respectively, the second roller 31 composed of the elastic body of the low hardness is deformed according to the load distribution so as to be shown by the figure and a contact part with the photosensitive belt 11a has a roughly straight line shape in the width direction. Therefore, the gap between the photosensitive belt 11a and the belt is eliminated. As the elastic body of the low hardness, a sponge, etc., made of rubber having the rubber hardness of 40° (JISA) or below, urethane foam, etc., can be used.