An illumination device includes a base board, an insulator, a conductor, a plurality of semiconductor light-emitting elements and a light-transmissive sealing member. The base board includes a surface and projection portions. The projection portion is formed to become gradually thicker from its end toward the surface of the base board. The insulator is formed on the surface. The conductor is formed on the insulator. The semiconductor light-emitting elements are mounted on the projection portions. The semiconductor light-emitting elements are electrically connected to the conductor via connection members. The sealing member covers the insulator, the projection portions, the semiconductor light-emitting elements and the connection members.