Abstract: A folding device for a milling machine includes a base having a workbench formed on top thereof, and two support parts are respectively located on two sides of the workbench so as to be connected to two support boards respectively. A pivot and a fixing bolt extend through the contact face and are fixed to the support part. A driving unit includes a transverse rail and a transverse shaft respectively connected between the two support boards. A slide is slidably connected with the transverse rail and the transverse shaft. A milling machine is connected to the slide which is movable between the two support boards. When the fixing bolts are removed, the milling machine is foldable toward the workbench about the two respective pivots to save transportation space and storage space required.