A wiring substrate includes a first wiring structure, a second wiring structure stacked on an upper surface of the first wiring structure, and an outermost insulating layer stacked on a lower surface of the first wiring structure. The outermost insulating layer covers a part of a bottom wiring layer of the wiring layers forming the first wiring structure. The second wiring structure has a wiring density higher than that of the first wiring structure. A volume ratio V1/V2 is from 0.8 to 1.5, where V1 represents the volume of the wiring layers forming the entire second wiring structure, and V2 represents the volume of the bottom wiring layer in the first wiring structure.