A circuit device which enables formation of a minute pattern while securing a current capacity and has excellent heat release properties, and a manufacturing method thereof are provided. In a circuit device of the present invention, among multiple wiring layers, a first wiring layer is formed of a thin first conductive pattern and a thick second conductive pattern. Therefore, formation of the minute patterns is realized while securing the current capacity. Moreover, a small-signal circuit element is mounted on the first conductive pattern, and a large-current circuit element is mounted on the second conductive pattern. Thus, circuit elements having different sizes of currents to be handled are mounted on the same board. Furthermore, heat release properties are improved by the second conductive pattern which is formed to be thick.