A reverse conveying apparatus which again conveys a sheet formed an image by an image forming portion to the image forming portion includes a plurality of roller grippers which supports a sheet formed an image, and a belt which moves the roller grippers to a receiving position where a sheet is received and a carry-out position where a supported sheet is conveyed out. A lock pin and a lock sleeve are spaced apart from the mounting pin and slidably extend for fitting within holes of respective racks to prevent removal of the mounting pin and the mounting sleeve from the racks. An LED portion has a blue LED which emits illumination light in the first wavelength band toward the switching filter. The MgO serves as stabilizers andor fluid loss control agents for VES-gelled fluids used to treat subterranean formations, e.