A conventional foldable electrical plug device generally includes top and bottom housing walls, and plug prongs disposed within a space defined by these walls. The plug prongs can be folded at about a 90 degree angle when plugged into a plug socket, and in this folded position, the plug prongs extend along a direction parallel to a direction along which the top and bottom housing walls are assembled together. However, when a user intends to remove the foldable electrical plug device from the plug socket, the user will apply a force in a direction parallel to the direction of assembling of the top and bottom housing walls. With that in mind, if the user grips the electrical plug device at an improper place, the top and bottom housing walls could be disassembled unintentionally. Thus, the conventional electrical plug device lacks the structural stability to be convenient for practical uses.