Provided is an on-vehicle illumination device which is compact, does not have a space therein, and is capable of realizing a complex curved surface shape. The on-vehicle illumination device includes a light-emitting element disposed on a wiring pattern on a substrate, and an outer lens layer made of a resin and mounted on the light-emitting element. The substrate has a shape curved along a curvature of the outer lens layer in a front-rear direction.