A light-source unit includes two LD arrays, each comprising four light-emitting points, a corresponding two coupling lenses coupling laser beams emitted from the two LD arrays, and a holding member integrally holding these LD arrays and coupling lenses rotatably approximately about optical axes on the laser beams are provided. Further, a scanning optical system is provided for deflecting the laser beams emitted from the light-source unit and imaging them onto the to-be-scanned surface.