A refrigerator comprising: a refrigerator compartment at an upper side and a freezer compartment at a lower side; a convertible compartment having a selectable temperature range and disposed between the refrigerator compartment and the freezer compartment; an evaporator disposed to the rear side of the freezer compartment for producing cold air for refrigerating interiors of the compartments; a fan located above the evaporator for forcibly delivering the produced cold air to individual storage compartments; and a duct unit formed behind the convertible compartment, the duct unit having an air duct (48,48a,48b,48c) for delivering the cold air to the refrigerator compartment and the convertible compartment, and a refrigerator compartment return duct (51 a) for returning the cold air delivered into the refrigerator compartment back to the evaporator, wherein the air duct (48, 48a, 48b, 48c) has a refrigerator compartment air duct for delivering the cold air to the refrigerator compartment, and a convertible compartment air duct for delivering the cold air to the convertible compartment, the refrigerator compartment air duct and the convertible compartment air duct are formed independently from each other, and the duct unit has the refrigerator compartment air duct, the convertible compartment air duct and the refrigerator compartment return duct (51 a) arranged laterally in a row, characterized in that the duct unit comprises an upper duct member and a lower duct member, each having a seal-connect portion for connecting the upper duct member and the lower duct member in a vertical direction, and that the exterior surfaces of the upper duct member and the lower duct member are sloped toward their seal-connect portions in a fashion to widen sectional areas at the seal-connect portions. a refrigerator compartment at an upper side and a freezer compartment at a lower side; a convertible compartment having a selectable temperature range and disposed between the refrigerator compartment and the freezer compartment; an evaporator disposed to the rear side of the freezer compartment for producing cold air for refrigerating interiors of the compartments; a fan located above the evaporator for forcibly delivering the produced cold air to individual storage compartments; and a duct unit formed behind the convertible compartment, the duct unit having an air duct (48,48a,48b,48c) for delivering the cold air to the refrigerator compartment and the convertible compartment, and a refrigerator compartment return duct (51 a) for returning the cold air delivered into the refrigerator compartment back to the evaporator, wherein the air duct (48, 48a, 48b, 48c) has a refrigerator compartment air duct for delivering the cold air to the refrigerator compartment, and a convertible compartment air duct for delivering the cold air to the convertible compartment, the refrigerator compartment air duct and the convertible compartment air duct are formed independently from each other, and the duct unit has the refrigerator compartment air duct, the convertible compartment air duct and the refrigerator compartment return duct (51 a) arranged laterally in a row, characterized in that the duct unit comprises an upper duct member and a lower duct member, each having a seal-connect portion for connecting the upper duct member and the lower duct member in a vertical direction, and that the exterior surfaces of the upper duct member and the lower duct member are sloped toward their seal-connect portions in a fashion to widen sectional areas at the seal-connect portions. a convertible compartment having a selectable temperature range and disposed between the refrigerator compartment and the freezer compartment; an evaporator disposed to the rear side of the freezer compartment for producing cold air for refrigerating interiors of the compartments; a fan located above the evaporator for forcibly delivering the produced cold air to individual storage compartments; and a duct unit formed behind the convertible compartment, the duct unit having an air duct (48,48a,48b,48c) for delivering the cold air to the refrigerator compartment and the convertible compartment, and a refrigerator compartment return duct (51 a) for returning the cold air delivered into the refrigerator compartment back to the evaporator, wherein the air duct (48, 48a, 48b, 48c) has a refrigerator compartment air duct for delivering the cold air to the refrigerator compartment, and a convertible compartment air duct for delivering the cold air to the convertible compartment, the refrigerator compartment air duct and the convertible compartment air duct are formed independently from each other, and the duct unit has the refrigerator compartment air duct, the convertible compartment air duct and the refrigerator compartment return duct (51 a) arranged laterally in a row, that the duct unit comprises an upper duct member and a lower duct member, each having a seal-connect portion for connecting the upper duct member and the lower duct member in a vertical direction, and that the exterior surfaces of the upper duct member and the lower duct member are sloped toward their seal-connect portions in a fashion to widen sectional areas at the seal-connect portions.