PURPOSE: To position a belt-like photosensitive body in a machine body and to easily attach it in a short time.

CONSTITUTION: An attaching frame is made to freely inserted and pulled out along a guide rail 13 provided in the machine body 12. The belt-like photosensitive body A is attachably/detachably attached to the attaching frame, and a positioning pin 20 on a machine body side is provided in the machine body 12 and a positioning pin 11 on a front side is provided in the photosensitive body A. An attaching plate 17 is disposed on the front side of the attaching frame and the photosensitive body A, and a lower hole 18 and an upper hole 19 in which the pins 11 and 20 are fitted are formed on the attaching plate 17, then a locking mechanism 21 supporting the attaching plate 17 in the machine body 12 is provided, and the mechanism 21 is constituted of a supporting plate 23 attached to the attaching plate 17, a bearing plate 25 attached to the machine body 12, and a locking bar 26 which is vertically and horizontally attached to the plate 25 and press-contacts with the supporting surface 27 of the supporting plate 23.