To obtain superior alignment accuracy by reducing the adjustment resolution to shift of resist in sub scanning directions.

A pair of eccentric cams 8, 8 in which each support shaft 46, 46 orthogonal to main scanning directions (arrow E directions) and orthogonal even to sub scanning directions (arrow C directions) is centered to be rotated and of which the cam faces 8a are in contact with lower surfaces of the both end portions of each lens case 16, and optical element sub scanning position adjusting mechanisms 30 having pressing plates 47 for adjusting eccentric amounts of the cams 8, 8 and feed screws 48 are provided on both end portions of the imaging lenses 69, 70, 71, 72, thereby the both end portions in the length directions of the imaging lenses 69-72 can be adjusted minutely in the sub scanning directions.