A semiconductor element mounting board includes: aboard having surfaces; a semiconductor element mounted on one of the surfaces of the board; a first layer into which the semiconductor element is embedded, the first layer being provided on the one surface of the board; a second layer provided on the other surface of the board, the second layer being constituted from the same material as that of the first layer, the constituent material of the second layer having the same composition ratio as that of the constituent material of the first layer; and surface layers provided on the first and second layers, respectively, each of the surface layers being formed from at least a single layer. In such a semiconductor element mounting board, each of the surface layers has rigidity higher than that of each of the first and second layers. It is preferred that in the case where a Young's modulus of each surface layer at 25° C. is defined as X GPa and a Young's modulus of the first layer at 25° C. is defined as Y GPa, the X and the Y satisfy a relation of 0.5≦X−Y≦13.