PURPOSE: To transmit radio waves and to improve insulation efficiency by composing the main body of the insulated tank of a radio wave transmitting material and providing a high refraction factor dielectric laminating body structure for which electric conductivity is low and the reflecting is high in infrared areas as a heat insulating member.

CONSTITUTION: This insulated tank is the dewar of duplex structure as the main body of the insulated tank provided with an inner tank 1 and an outer tank 3 and between these inner tank 1 and outer tank 3, a vacuum heat insulation part 5 is formed. In the heat insulation part 5, a heat insulating member 9 is provided to prevent heat from flowing in by the radiation of heat. The heat insulating member 9 is composed of high refracting factor dielectric board members and a plastic spacer for providing a gap between the board members and the laminating body structures adhered by an adhesive are adhered almost without any space by using the adhesive so as to be laminated structure. Inside the inner tank 1, liquid nitrogen 14 is stocked and content in the inner tank 1 are cooled to the temperature of liquid nitrogen by the liquid nitrogen 14.