A one-dimensional illumination apparatus includes: a light source including a plurality of laser devices arrayed one-dimensionally; a wavefront dividing unit including one or more cylindrical lens arrays for dividing a wavefront of light emitted from the light source and superimposing divided wavefronts; a waveform superimposing unit for introducing light from the wavefront dividing unit to an object and superimposing divided wavefronts; and a polarization converting unit for rotating a plane of polarization of one laser beam of a pair of adjacent laser beams divided by the wavefront dividing unit. The polarization converting unit is located right in front of or right behind an optical element through which laser light from the light source finally passes in the wavefront dividing unit.