Conventionally, an electrographic image forming apparatus, such as a copying machine or a printer, uses an optical scanning device composed of a laser scanning unit (LSU) or the like to form an electrostatic latent image on a surface of an image carrier, such as a photosensitive drum, and develops this electrostatic latent image by a toner, thereby performing an image forming operation. 
The optical scanning device includes, for example, a light source outputting a laser light, a lens (e.g. a collimator lens or a cylindrical lens) concentrating the laser light outputted from this light source, a deflector, such as a polygon mirror, deflecting the laser light concentrated by this lens, and an optical element, such as a lens or a mirror, leading the laser light deflected by this deflector to the image carrier. 
Moreover, when scanning the laser light from the optical scanning device onto the image carrier to form the electrostatic latent image, a problem, that this electrostatic latent image is curved or inclined in a sub-scanning direction of the laser light, may occur and color drift may be caused in color registration of a formed image.  Thereupon, there is an optical scanning device adjusting component so as to prevent the problem of these scanning curving or scanning inclining. 
For example, in Patent Document 1, an optical scanning device of an image forming apparatus includes a longitudinal lens correcting a plane tilt of a polygon mirror and is provided with an inclination adjustment driving part and a curve adjustment driving part with respect to this longitudinal lens to adjust inclination and curve of a scanning line conducting via the longitudinal lens.  The curve adjustment driving part warps the longitudinal lens by a scanning line curve adjusting screw to adjust scanning line curve. 
Moreover, in Patent Document 2, an optical scanning device of an image forming apparatus includes a reflection mirror leading a laser light to a photoreceptor and is provided with a curve correcting mechanism and an inclination correcting mechanism with respect to this reflection mirror to correct curve and inclination of a scanning line reflected by the reflection mirror.  The curve correcting mechanism warps the reflection mirror by a curve adjusting screw to correct curve of the scanning line.