A front panel assembly includes an inner cover plate having two first positioning pins, and a sliding door mechanism including a pair of slide rails each provided on a lateral side of the inner cover plate and having top and bottom ends. The first positioning pins are disposed intermediate of the pair of the slide rails. A door panel is slidable upward and downward along the slide rails, and has two second positioning pins. Two spring elements are disposed between the door panel and the inner cover plate. Each spring element has a first connecting end connected pivotally to a corresponding first positioning pin, and a second connecting end connected pivotally to a corresponding second positioning pin.