An electronic component built-in substrate, includes, a substrate having an opening portion, a first wiring layer formed in the substrate, an electronic component arranged in the opening portion, a first insulating layer formed on one face of the substrate and sealing the electronic component, a second insulating layer formed on other face of the substrate, a second wiring layer formed on the first insulating layer, and a third wiring layer formed on the second insulating layer. The first insulating layer is formed of an inner insulating layer covering the one face of the substrate and filling an inside of the opening portion, and an outer insulating layer formed on the inner insulating layer.