PURPOSE: A composite window is provided to easily couple/decouple a sash unit to/from a decoration unit using an elastic connection unit and to improve heat insulating and soundproofing properties. CONSTITUTION: A composite window comprises a sash unit(110), a decoration unit(120), and elastic connection units(130). One or more coupling protrusions(111) are formed in the sash unit. The decoration unit is coupled to the sash unit. Housing grooves(121), in which the coupling protrusions are inserted, are formed on the decoration unit. The elastic connection units are located between the coupling protrusions and the housing grooves when the coupling protrusions are inserted into the housing grooves and fix the sash unit to the decoration unit.
