There is provided a multilayer wiring substrate on which at least one semiconductor element is mounted. The multilayer wiring substrate includes: a baseboard; a first wiring layer formed on the baseboard and having a plurality of first wiring portions; an insulating layer formed on the baseboard; a second wiring layer formed on the insulating layer and having a plurality of second wiring portions, the second wiring portions being electrically connected to each other via a conductor wire, the conductor wire being arranged within the insulating layer three-dimensionally in a curved manner; and conductor portions configured to pass through the insulating layer and connecting the first wiring portions and the second wiring portions.