A manufacturing method of a reinforcing structure includes: preparing a stringer having a fiber exposure surface; arranging an insulation protection material to cover at least a part of the fiber exposure surface; arranging the stringer on a skin having an uncured resin component; and curing the skin after the arranging the stringer. The insulation protection material includes a composite material having a resin component and an insulative fiber component. The curing the skin includes curing the skin and the insulation protection material at the same time. In the manufacturing method of a reinforcing structure, an edge glow discharge can be prevented without increasing a manufacturing process.