An organic insulating material includes a prepolymer of a cage structure compound having a polymerizable unsaturated bond-containing group and a cage structure with an adamantane structure as the minimal unit. The prepolymer has a number-average molecular weight of between 2,000 and 500,000 based on polystyrene and measured by gel permeation chromatography. The prepolymer includes unsaturated bonds produced by reaction between the polymerizable unsaturated bonds and the unreacted polymerizable unsaturated bonds. The prepolymer has a residue rate of unreacted polymerizable unsaturated bonds of between 20% and 80%.