Provided is a circuit device that allows a plurality of circuit boards, which are stacked each other and arranged in a case member, to be sealed with a resin effectively, and a method of manufacturing the same. In a hybrid integrated circuit device, a first circuit board is overlaid with the second circuit board and both of the boards are fitted into the case member. 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, an opening is provided in a side wall part of the case member, and an internal space of the case member communicates with the outside through this opening. Accordingly, in the resin sealing step, a sealing resin can be injected into the internal space of the case member from the outside through this opening.