A refrigerator comprising: a first main body which has a first cavity provided by a first plate member and a second plate member; a second main body which has a second cavity provided by a third plate member and a fourth plate member; a first sealing part which seals the first plate member and the second plate member, and a second sealing part which seals the third plate member and the fourth plate member, so that the first plate member and the third plate member define at least a portion of a wall for a first space, the second plate member and the fourth plate member define at least a portion of a wall for a second space, and a third space which has a temperature between a temperature of the first space and a temperature of the second space and is a space in a vacuum state being provided between the first and the second plate members (10, 20) and between the third and the fourth plate members; a supporting unit configured to maintain the third space; a first heat resistance unit for reducing a heat transfer amount between the first plate member and the second plate member; a second heat resistance unit for reducing a heat transfer amount between the third plate member and the fourth plate member; a port for discharging air in the third space; a door (3a, 3b) configured to close the openings of the first main body and the second main body; a gasket which is installed to at least one of the door (3a, 3b) and the main bodies (2a, 2b) so as to seal a portion in which the door and the main bodies are in contact with each other; and a mullion provided at a boundary part of the main bodies (2a, 2b), characterized in that: the mullion includes a supporting block provided at each vertex portion of a two-dimensional flat surface constituting the boundary part of the main bodies (2a, 2b), and a panel member to close an opening between the supporting blocks; wherein each supporting block is positioned between the first main body and the second main body and fastened to outer surfaces of the second plate member and the fourth plate member, and each supporting block includes an opening surface to provide access from outside therethrough for fastening and dismounting through an outer surface of the refrigerator. a first main body which has a first cavity provided by a first plate member and a second plate member; a second main body which has a second cavity provided by a third plate member and a fourth plate member; a first sealing part which seals the first plate member and the second plate member, and a second sealing part which seals the third plate member and the fourth plate member, so that the first plate member and the third plate member define at least a portion of a wall for a first space, the second plate member and the fourth plate member define at least a portion of a wall for a second space, and a third space which has a temperature between a temperature of the first space and a temperature of the second space and is a space in a vacuum state being provided between the first and the second plate members (10, 20) and between the third and the fourth plate members; a supporting unit configured to maintain the third space; a first heat resistance unit for reducing a heat transfer amount between the first plate member and the second plate member; a second heat resistance unit for reducing a heat transfer amount between the third plate member and the fourth plate member; a port for discharging air in the third space; a door (3a, 3b) configured to close the openings of the first main body and the second main body; a gasket which is installed to at least one of the door (3a, 3b) and the main bodies (2a, 2b) so as to seal a portion in which the door and the main bodies are in contact with each other; and a mullion provided at a boundary part of the main bodies (2a, 2b), the mullion includes a supporting block provided at each vertex portion of a two-dimensional flat surface constituting the boundary part of the main bodies (2a, 2b), and a panel member to close an opening between the supporting blocks; wherein each supporting block is positioned between the first main body and the second main body and fastened to outer surfaces of the second plate member and the fourth plate member, and each supporting block includes an opening surface to provide access from outside therethrough for fastening and dismounting through an outer surface of the refrigerator.