An antenna-attached substrate according to the present disclosure includes a substrate layer, a lower antenna element that is disposed in the substrate layer, an antenna-holding layer that is stacked on an upper surface of the substrate layer, and an upper antenna element that is disposed in the antenna-holding layer and that faces an upper surface of the lower antenna element. The antenna-holding layer is composed of a dielectric material having a relative dielectric constant lower than that of the substrate layer. A lower surface, a side surface, and an upper surface of the upper antenna element are covered by the antenna-holding layer.