A lighting device (1) is configured to include: an elongated flat substrate (2); a plurality of semiconductor light sources (3) arranged on the flat substrate in a longitudinal direction of the flat substrate; and a lens plate (4) disposed to face the semiconductor light sources, wherein the lens plate includes a lens-light-incident surface facing the semiconductor light sources and includes a lens-light-emitting surface, a first lens section (5) is formed on one of the lens-light-incident surface and the lens-light-emitting surface and distributing the light emitted by the semiconductor light source in the longitudinal direction, a second lens section (9) is formed on the other one of the lens-light-incident surface and the lens-light-emitting surface for distributing the light emitted by the semiconductor light sources in a width direction, and the first lens section has a curvature surface unit including two or more convex section curvature surfaces having different curvature radii and formed adjacent in the longitudinal direction, each convex section's curvature surface is disposed inside a facing area facing an area corresponding to a width of each semiconductor light source in the longitudinal direction.