An assembly device includes a base having a supporting portion upon which an isolation cover and a main body are disposed. A press-fitting mechanism is movably connected to the base, and includes a press-fitting portion facing the supporting portion and disposed corresponding in position to the supporting portion, and further portions for guiding and bending second positioning portions. The further portions are movably disposed on external side faces of the press-fitting portion. The press-fitting mechanism also has first portions for holding the further portions to the external side faces of the press-fitting portion, and has second portions passing through upper ends of the further portions. A drive mechanism is disposed at the base and has a drive portion connected to the press-fitting mechanism, for driving the press-fitting mechanism to move towards the supporting portion via the drive portion, so as to bend and fasten ends of second positioning portions.