A door operating mechanism for opening and closing a door with respect to a vertical opening of a case includes a hinge structure for selectively connecting an upper end of the door to the case in a hinged manner so as to guide a pivotal movement of the door between a vertically closed position and a horizontally extended open position where the door is extended outwardly from the case. There is provided a guide structure for guiding the horizontal movement of the door between the horizontal extended open position and a horizontal retracted open position where the door is received in the case. Thus, the door can be suitably received in the case, so that the opened door will not be obstructive.