Provided is a circuit device capable of increasing the packaging density and also suppressing the thermal interference between incorporated circuit elements. In a hybrid integrated circuit device, a first circuit board and a second circuit board are incorporated into a case member being arranged in a way that the first circuit board is overlaid with the second circuit board. A first circuit element is arranged on the upper face of the first circuit board and a second circuit element is arranged on the upper face of the second circuit board. In addition, inside the case member, a hollow portion (internal space) which is not filled with a sealing resin is provided, and this hollow portion communicates with the outside through a communicating opening, which is provided by partially opening the case member.