To provide an optical scanner capable of stably scanning with high accuracy using a plurality of light rays.

An optical scanner comprises two light sources, two pre-deflector optical systems, a polygon mirror, and two scanning optical systems. Each light source and each pre-deflector optical system are held by a holding member to be fabricated into a unit. Each pre-deflector optical system has a cylindrical lens, and the cylindrical lenses (2204a and 2204b) are adhered to a common side plate of the holding member using each entire face of each one side end face of the cylindrical lenses in a direction corresponding to a main scanning direction. In such a structure, a moving direction of each cylindrical lens caused by a change in environmental temperature corresponds to the direction corresponding to the main scanning direction, so as to prevent a light spot on the surface of a photosensitive drum from becoming thick in a sub-scanning direction, thereby preventing degradation in optical characteristics even when environmental temperature changes.