To provide a method of manufacturing a highly reliable circuit device realizing a smaller, thinner and lighter configuration. In the method of manufacturing a circuit device according to the invention, a resin sealed body is separated from a supporting substrate, after the resin sealed body containing a circuit device is formed on a top surface of the supporting substrate. Therefore, manufacture of a circuit device having no substrate becomes possible and it realizes a thinner and lighter circuit device with improved heat dissipation. Moreover, since sealing with a sealing resin can be performed on the supporting substrate, warps, caused by the differences in thermal expansion coefficients between the sealing resin and conductive patterns and between the sealing resin and circuit components, can be prevented. Hence, it becomes possible to prevent flaking of conductive patterns from the substrate and a poor contact between the conductive patterns and a metal thin wire, and consequently to manufacture a highly reliable circuit device.