A refrigerator comprising: a main body having a storage space therein; a first door hinged to the main body for opening and closing the storage space; a door frame provided at the first door; a second door hinged to the first door, the second door having a side wall, at least a portion of which is inserted into the door frame, and a catching part provided in the side wall; and a locking device for selectively allowing the second door to be turned with respect to the first door, characterized in that the locking device comprises: a moving member, a displacement of which is changed in a horizontal direction depending on an open or closed state of the first door; and a catching member, a displacement of which is changed in a vertical direction depending on the displacement of the moving member, whereby a protruding length of the catching member from the door frame is changed, the catching member being selectively caught in the catching part, wherein a first inclined surface is provided at the moving member; and a second inclined surface provided at the catching member so as to slide with respect to the first inclined surface in a state of contacting the first inclined surface, and wherein the first inclined surface is in contact with the second inclined surface in a state in which the first door is opened and in the state in which the first door is closed. a main body having a storage space therein; a first door hinged to the main body for opening and closing the storage space; a door frame provided at the first door; a second door hinged to the first door, the second door having a side wall, at least a portion of which is inserted into the door frame, and a catching part provided in the side wall; and a locking device for selectively allowing the second door to be turned with respect to the first door, characterized in that the locking device comprises: a moving member, a displacement of which is changed in a horizontal direction depending on an open or closed state of the first door; and a catching member, a displacement of which is changed in a vertical direction depending on the displacement of the moving member, whereby a protruding length of the catching member from the door frame is changed, the catching member being selectively caught in the catching part, wherein a first inclined surface is provided at the moving member; and a second inclined surface provided at the catching member so as to slide with respect to the first inclined surface in a state of contacting the first inclined surface, and wherein the first inclined surface is in contact with the second inclined surface in a state in which the first door is opened and in the state in which the first door is closed. a moving member, a displacement of which is changed in a horizontal direction depending on an open or closed state of the first door; and a catching member, a displacement of which is changed in a vertical direction depending on the displacement of the moving member, whereby a protruding length of the catching member from the door frame is changed, the catching member being selectively caught in the catching part, wherein a first inclined surface is provided at the moving member; and a second inclined surface provided at the catching member so as to slide with respect to the first inclined surface in a state of contacting the first inclined surface, and wherein the first inclined surface is in contact with the second inclined surface in a state in which the first door is opened and in the state in which the first door is closed.