To provide a modification device that can modify an object to be subjected to image formation by an image forming device such as a copying machine, a facsimile machine and a printer, by bringing plasma into contact with the object to be processed while conveying the same, and that avoids or suppresses a leak of a product occurring as the plasma is generated while securing use efficiency of a component effective to the modification, and to provide an image forming device, a preprocessing device, and a postprocessing device each provided with the modification device.

The modification device includes: a cover member 60 connected to suction means P for sucking a product generated as the plasma is generated caused by a discharge electrode 84 together with air and covering the discharge electrode 84; and an electrode cover 98. The electrode cover 98 includes: an electrode coating part 98a covering the discharge electrode 84 inside the cover member 60; and an flange part 98b which is united with the electrode coating part 98a at a position downstream from the electrode coating part 98a in a conveyance direction B1 of the object to be processed and is provided opposite the object to be processed S.