A refrigerator includes a main body provided with storage chambers having doors, one of the doors being provided with an opening, the opening having at least one stepped plane; a rack installed in the storage chamber at a height corresponding to that of the lower end of the opening; a sub door to open and close the opening; and a connection member to prevent a height difference between a rear surface of the sub door and the opening. The connection member is configured to slide relative to the sub door to cover the at least one stepped plane, whereby the connection member closes the at least one stepped plane when the sub door is closed, and opens the at least one stepped plane when the sub door is opened so that the rear surface of the sub door and the connection member form substantially a level plane with the rack.