A level adjustment device includes a main body, four shaft seats, two adjusting elements, two actuating gears, and a supporting plate. The main body has a side surface and an upper surface connected to the side surface. The main body defines two slots in the side surface. Each two shaft seats are positioned at two opposite sides of a corresponding one of the slots and extend outwards from the side surface. Each of the adjusting elements includes a toothed portion and a supporting portion, the toothed portion movably received in the slot and the supporting portion protruding out of the upper surface. Each of two actuating gears is rotatably sleeved between two corresponding shaft seats and meshes with the toothed portion. The supporting plate is supported on the two adjustment elements above the upper surface.