Provided is a circuit device capable of increasing the packaging density and preventing the thermal interference between circuit elements to be incorporated. In a hybrid integrated circuit device, a first circuit board and a second circuit board are fitted into a case member in a way that the first circuit board is overlaid with the second circuit board. A first circuit element is arranged on the upper surface of the first circuit board and a second circuit element is arranged on the upper surface of the second circuit board. Furthermore, inside the case member, provided is a hollow portion that is not filled with a sealing resin. Such a configuration prevents the second circuit element, which is a microcomputer, from operating unstably due to a heat generated in the first circuit element, which is a power transistor, for example.