is not shown fig2 shows the positions of the folding minors 32 and 33 before and after moving the folding minors 32 and 33 in the direction of the arrow a with the xy stage 35 and optical paths of laser beams irradiated from the respective light source parts 1 in fig2 optical paths of the respective laser beams before shifting the folding mirrors 32 and 33 are shown by dashed lines and optical paths of the respective laser beams after shifting the folding mirrors 32 and 33 are shown by solid lines when the optical paths of the respective laser beams before and after shifting the folding mirrors 32 and 33 are overlapped the optical paths are shown by solid lines additionally the folding minors 32 and 33 before shifting are shown with dashed lines and the folding mirrors 32 u2032 and 33 u2032 after shifting are shown with solid lines respectively as shown in fig2 entrance positions of laser beams with respect to the folding mirrors 32 and 33 are fluctuated before and after shifting the folding minors 32 and 33 therefore a length of such a laser beam before and after shifting the folding minors 32 and 33 is fluctuated on the other hand entrance positions and angles of laser beams with respect to the condensing lens 34 are substantially not fluctuated before and after shifting the folding mirrors 32 and 33 namely in the two dimensional scanning optical device 100 the length of the optical path from the condensing lens 31 to the condensing lens 34 hereinafter written as u201c an optical path length between condensing lenses u201d for convenience can be adjusted in accordance with amounts of the shifts of the folding minors 32 and 33 while the positions of the entrance pupil.