A wiring board is disclosed. The wiring board includes a substrate including a first element, a diffusion layer in contact with the substrate and including a first metal element, and a first metal film in contact with the diffusion layer and including a second metal element. The diffusion layer has at least a region including the first element and the first metal element and a region including the first metal element and the second metal element. A concentration of the second metal element in the diffusion layer may decrease as it approaches the substrate in a depth direction. A concentration of the first element in the diffusion layer may decrease as it approaches the first metal film in the depth direction.