A wiring substrate includes: a core substrate made of glass and having: a first surface; a second surface opposite to the first surface; and a side surface between the first surface and the second surface; and an insulating layer and a wiring layer, which are formed on at least one of the first surface and the second surface of the core substrate. A plurality of concave portions are formed in the side surface of the core substrate to extend from the first surface to the second surface, and a resin is filled in the respective concave portions.