To obtain a wide passenger compartment space, the thickness of a heat insulating acoustical layer is reduced, and for this purpose, a comfortable in-car environment is obtained by using a vacuum insulating panel which combines high heat insulating performance and sound insulating performance. A heat insulating acoustical layer 20 is formed on one surface of a lightweight alloy structure 10 of double skin construction by using a vacuum insulating panel 21 as a middle member and sandwiching two surfaces of the panel with elastic sound absorbing materials 22, 23 made of a nonwoven fabric or a foamed body, and the heat insulating acoustical layer is covered with an interior material 24. Owing to this construction, the transmission loss of a noise which transmits from the double skin structure side is improved by the mutual actions of the elasticity of the sound absorbing material and the rigidity of the vacuum heat insulating panel.