A refrigerator comprising: a cabinet defining a first storage compartment in which a food is stored, a main door rotatably mounted on the cabinet to open or close the first storage compartment and having an opening; a door hinge connecting an upper end of the main door to a top surface of the cabinet; a separate hinge disposed on a lower end of the main door to rotatably mount the main door to the cabinet; an accommodation device that is accessible through an opening of the main door, the accommodation device defining a second storage compartment in a back surface of the main door, a sub door opening or closing the opening, an upper hinge rotatably mounting the sub door on the main door, the upper hinge having one end coupled to the upper end of the main door and the other end coupled to atop surface of the sub door; a lower hinge disposed on a lower end of the sub door and mounted on the main door to rotatably support the sub door; a locking member disposed on a back surface of the sub door and protruding from a central portion of one end of the back surface of the sub door; a locking unit disposed on one side of a front surface of the main door to be selectively coupled to the locking member; and a door opening assembly configured to restrict the sub door and the main door or release the restriction of the sub door from the main door, characterized in that the door opening assembly includes: a manipulation member manipulated by a user and disposed on a lower end of the sub door; a push rod selectively protruding backward from an inside of the sub door; and a connection member connected to the manipulation member so that the push rod is operable and having an upper end contacting the push rod and a lower end contacting the manipulation member, wherein the connection member is configured to be moved upward by a manipulation of the manipulation member and to push the push rod backward such that the locking member is released from the locking unit. a cabinet defining a first storage compartment in which a food is stored, a main door rotatably mounted on the cabinet to open or close the first storage compartment and having an opening; a door hinge connecting an upper end of the main door to a top surface of the cabinet; a separate hinge disposed on a lower end of the main door to rotatably mount the main door to the cabinet; an accommodation device that is accessible through an opening of the main door, the accommodation device defining a second storage compartment in a back surface of the main door, a sub door opening or closing the opening, an upper hinge rotatably mounting the sub door on the main door, the upper hinge having one end coupled to the upper end of the main door and the other end coupled to atop surface of the sub door; a lower hinge disposed on a lower end of the sub door and mounted on the main door to rotatably support the sub door; a locking member disposed on a back surface of the sub door and protruding from a central portion of one end of the back surface of the sub door; a locking unit disposed on one side of a front surface of the main door to be selectively coupled to the locking member; and a door opening assembly configured to restrict the sub door and the main door or release the restriction of the sub door from the main door, characterized in that the door opening assembly includes: a manipulation member manipulated by a user and disposed on a lower end of the sub door; a push rod selectively protruding backward from an inside of the sub door; and a connection member connected to the manipulation member so that the push rod is operable and having an upper end contacting the push rod and a lower end contacting the manipulation member, wherein the connection member is configured to be moved upward by a manipulation of the manipulation member and to push the push rod backward such that the locking member is released from the locking unit. a manipulation member manipulated by a user and disposed on a lower end of the sub door; a push rod selectively protruding backward from an inside of the sub door; and a connection member connected to the manipulation member so that the push rod is operable and having an upper end contacting the push rod and a lower end contacting the manipulation member, wherein the connection member is configured to be moved upward by a manipulation of the manipulation member and to push the push rod backward such that the locking member is released from the locking unit.