To provide an image forming apparatus in which the focusing position and the conjugate relation are corrected, regardless of the imaging magnification, between a deflecting face and a face to be scanned in an optical scanner, and to provide a method of adjusting the image forming apparatus.

The image forming apparatus is provided with an optical scanner which is so constituted that luminous flux, emitted from a light source 10, is focused into a linear image that extends in the main scanning direction on the surface of a deflector 16 by means of a light source side optical system 15; the focused luminous flux is deflected by the deflector 16; the deflected luminous flux is focused into a spot, having a predetermined shape on a face to be scanned with an imaging optical system 18, an image is formed in a recording medium by the spot; and the distance d between the optical scanner and the recording medium is adjustable.