A refrigerator, comprising: a cabinet defining a first storage chamber; and a main door coupled to the cabinet, the main door comprising: a first door opening and closing the first storage chamber; and a storage case coupled to an interior side of the first door, the storage case defining a second storage chamber; wherein the main door further comprises: an opening formed through the first door, in communication with an open front of the second storage chamber; a second door coupled to the first door at a position corresponding to the open front of the second storage chamber to open and close the second storage chamber; a first basket provided in the storage case, wherein the first basket is vertically movable within the storage case; and at least one rail extending vertically in the second storage chamber to guide movement of the first basket, wherein, in a first mode of the main door, the first storage chamber is accessible using the first door and the second storage chamber is inaccessible, and in a second mode of the main door the second storage chamber is accessible using the second door and the first storage chamber is inaccessible, characterized by an operation mechanism coupled between the first basket and the at least one rail to selectively restrict movement of the first basket, wherein the operation mechanism is partially exposed via the opening in the first door when the second door is rotated away from the first door in the second mode. a cabinet defining a first storage chamber; and a main door coupled to the cabinet, the main door comprising: a first door opening and closing the first storage chamber; and a storage case coupled to an interior side of the first door, the storage case defining a second storage chamber; a first door opening and closing the first storage chamber; and a storage case coupled to an interior side of the first door, the storage case defining a second storage chamber; wherein the main door further comprises: an opening formed through the first door, in communication with an open front of the second storage chamber; a second door coupled to the first door at a position corresponding to the open front of the second storage chamber to open and close the second storage chamber; a first basket provided in the storage case, wherein the first basket is vertically movable within the storage case; and at least one rail extending vertically in the second storage chamber to guide movement of the first basket, wherein, in a first mode of the main door, the first storage chamber is accessible using the first door and the second storage chamber is inaccessible, and in a second mode of the main door the second storage chamber is accessible using the second door and the first storage chamber is inaccessible, characterized by an operation mechanism coupled between the first basket and the at least one rail to selectively restrict movement of the first basket, wherein the operation mechanism is partially exposed via the opening in the first door when the second door is rotated away from the first door in the second mode. an opening formed through the first door, in communication with an open front of the second storage chamber; a second door coupled to the first door at a position corresponding to the open front of the second storage chamber to open and close the second storage chamber; a first basket provided in the storage case, wherein the first basket is vertically movable within the storage case; and at least one rail extending vertically in the second storage chamber to guide movement of the first basket, wherein, in a first mode of the main door, the first storage chamber is accessible using the first door and the second storage chamber is inaccessible, and in a second mode of the main door the second storage chamber is accessible using the second door and the first storage chamber is inaccessible, characterized by an operation mechanism coupled between the first basket and the at least one rail to selectively restrict movement of the first basket, wherein the operation mechanism is partially exposed via the opening in the first door when the second door is rotated away from the first door in the second mode.