A light source module includes a substrate, a plurality of light emitting devices disposed along a line on the substrate, and a lens. The lens extends in a long-axis direction in which the plurality of light emitting devices are aligned to cover the substrate and the plurality of light emitting devices, and has end sides opened at opposing ends of the lens in the long-axis direction. The lens has a first surface to which light from the plurality of light emitting devices is made incident, and a second surface allowing light made incident through the first surface to be radiated outwardly. The lens has a variable thickness, measured as a distance between the first surface and the second surface, in a cross-section of the lens along a plane orthogonal to the long-axis direction.