Patent ID: 7599105

Claim:
An optical scanning device, comprising: a light source unit configured to irradiate a light beam; an oscillating mirror configured to deflect the light beam from the light source unit to scan a scan object surface backward and forward, the oscillating mirror being supported by a torsion beam; a focusing optical system configured to focus the light beam deflected by the oscillating mirror on the scan object surface; a housing unit configured to position the light source unit, the oscillating mirror, and the focusing optical system in a plane substantially orthogonal to at least the torsion beam; an oscillating mirror driving unit configured to rotate the oscillating mirror around a rotational axis; a window member configured to transmit the light beam incident on and reflected from the oscillating mirror; and a sealing member configured to hold the window member and seal a space in which the oscillating mirror is mounted, wherein a position of the window member is fixed in the plane substantially orthogonal to the torsion beam such that the angle, in the main scanning direction between a light beam from a light source unit and the normal line of the window member satisfies a predetermined relationship, wherein the oscillating mirror and the window member are arranged at predetermined angles with respect to the light beam from the light source and an optical axis of the focusing optical system, wherein when the oscillating mirror is in a non-rotated position, a first incident angle in a main scanning direction between the light beam from the light source unit and a normal line of the window member is greater than a second incident angle in a main scanning direction between the light beam from the light source unit and a normal line of the oscillating mirror, wherein the position of the rotational axis of the oscillating mirror is fixed in the plane orthogonal to the torsion beam such that the rotational axis of the oscillating mirror meets the intersection point of a light beam from a light source unit and a light axis of the focusing optical system.