A wiring board includes an insulating layer; and a wiring layer embedded in the insulating layer at one surface side of the insulating layer, one surface of the wiring layer being exposed from one surface of the insulating layer, the wiring layer including a first portion and a second portion whose width is wider than that of the first portion, one surface of the first portion and one surface of the second portion being flush with each other, and the first portion being thinner than the second portion.