A wiring board is constructed such that a base layer constituted of photosensitive polyimide, a conductor layer constituted of copper, and a cover layer constituted of photosensitive polyimide are formed in this order on a stainless layer. On an electronic part mounting portion, a plurality of lands are formed so as to correspond to electrode terminals of an electronic part to be mounted. On the periphery of the electronic part mounting portion, an underfill diffusion preventing portion formed by removing the cover layer in a trench shape is provided so as to surround the periphery thereof.