To provide an optical scanner which uses a light source unit emitting a plurality of beams and a collimator unit, to provide an image forming apparatus equipped with the optical scanner, and to improve not only an image forming efficiency, but also a resolution simply, surely and at a low cost without causing the deterioration of image.

The optical scanner uses the light source unit which outputs a plurality of beams from a multilaser light source on which a multilaser array is provided. The optical scanner is characterized in that a compression optical system which compresses the distance between the plurality of beams in a subscanning direction is provided between a multilaser light source and a collimator lens which substantially parallelize the plurality of beams outputted from the multilaser light source. The image forming apparatus is provided with the optical scanner.