A wiring board 10 includes a wiring board main body 11 having a semiconductor device attaching pad 21 on which a semiconductor device 14 is attached, a dielectric layer 22 provided with the semiconductor device attaching pad 21, and a semiconductor device attaching area A in which the semiconductor device 14 is attached, and a stiffener bonded to a surface 22A of the dielectric layer 22 on the side where the semiconductor device attaching pad 21 is formed and having a semiconductor device attaching through portion 12A to expose the semiconductor device attaching area A, characterized in that a notch portion 41 for exposing the surface 22A of the dielectric layer 22 in a part located outside the semiconductor device attaching area A is provided on the outer periphery of the stiffener 12.