A refrigerator comprising: a cabinet having a storage chamber therein; a main door pivotably mounted to the cabinet and to open or close the storage chamber, the main door having an opening provided at the front surface of the main door, a stepped portion provided around the opening, and a sub-storage chamber provided at the opening of the main door; a sub-door mounted to the main door to allow opening or closing of the opening so as to allow a user to have access to the sub-storage chamber; at least one hinge (260, 270), one end of the at least one hinge pivotably mounted to the main door and the other end of the at least one hinge mounted to the sub-door, at least one hinge having a bent structure (272, 273) at an intermediate portion thereof to pivotably support the sub-door with respect to the main door, characterized by a handle groove provided at one side of an upper portion of the sub-door; a hook member pivotably mounted to one side of the handle groove; an engagement groove provided at the front surface of the main door such that the hook member is selectively engageable in the engagement groove; and a lever member mounted to be pivotable by a user pulling the lever member with respect to a horizontal pivot axis in the handle groove, to pivot the hook member so as to release an engagement state of the hook member in the engagement groove, wherein the sub-door has opposite side surfaces with front portions protruding forwards of a front surface of the main door and has a greater width between the front portions of opposite side surfaces than the width of the opening and the width of the stepped portion to cover the stepped portion by the opposite side surfaces. a cabinet having a storage chamber therein; a main door pivotably mounted to the cabinet and to open or close the storage chamber, the main door having an opening provided at the front surface of the main door, a stepped portion provided around the opening, and a sub-storage chamber provided at the opening of the main door; a sub-door mounted to the main door to allow opening or closing of the opening so as to allow a user to have access to the sub-storage chamber; at least one hinge (260, 270), one end of the at least one hinge pivotably mounted to the main door and the other end of the at least one hinge mounted to the sub-door, at least one hinge having a bent structure (272, 273) at an intermediate portion thereof to pivotably support the sub-door with respect to the main door, characterized by a handle groove provided at one side of an upper portion of the sub-door; a hook member pivotably mounted to one side of the handle groove; an engagement groove provided at the front surface of the main door such that the hook member is selectively engageable in the engagement groove; and a lever member mounted to be pivotable by a user pulling the lever member with respect to a horizontal pivot axis in the handle groove, to pivot the hook member so as to release an engagement state of the hook member in the engagement groove, wherein the sub-door has opposite side surfaces with front portions protruding forwards of a front surface of the main door and has a greater width between the front portions of opposite side surfaces than the width of the opening and the width of the stepped portion to cover the stepped portion by the opposite side surfaces.