PURPOSE: To provide a device for detecting the positional information of a traveling object without being affected by the secular change accompanying the wear of the position detecting mark surface.

CONSTITUTION: The mark 5 for detecting the position of the seam 4 is composed at the end part of the photoreceptor belt 1. The mark 5 is constituted of the multilayer of the uppermost layer 5-1, the intermediate layer 5-2 and the lowermost layer 5-3. The mark surface is rubbed and worn by the mark cleaning member. When the uppermost layer 5-1 is worn off, the intermediate layer 5-2 located below is exposed.