PURPOSE: To eliminate the need to provide an additional optical element by providing a light source which emits a light beam, a medium which receives the light beam, and two spiral optical devices arranged between the light source and medium.

CONSTITUTION: This device is equipped with the light source 10 like a laser emitting the light beam and two spiral optical elements 12 and 14 having specular reflecting spiral surfaces 16 and 18 which receive the light beam 11 and reflect the light beam 11 to the medium 20. Then the spiral surfaces 16 and 18 have pitch angles α1 and α2 respectively, and the pitch angles α1 and α2 are so prescribed that the reflecting surfaces are normally orthogonal to each other at reflection points; and those pitch angles partially correct aberrations that the beam has since the spiral surface 16 is not flat.