An object of the present invention is to provide a millimeter wave radar device and module that provides a hollow structure while assuring adequate moisture resistance.A multilayer substrate on which at least one millimeter wave MMIC is mounted and a cap for forming a hollow around the MMIC are joined together with an adhesive or other similar organic member to obtain a high-frequency characteristic. The resulting assembly is housed in a case and covered with a moisture resistance by a gelled organic resin. The nonairtight structure obtained in this manner permits the use of low-cost members and provides increased productivity.