Color image forming device

A color image forming device for forming a color image on a surface of a sheet-like medium by overlapping images of various colors, comprising:

• a plurality of optical systems, each including a laser light source for emitting a laser beam according to an image signal each color;
• a plurality of photosensitive bodies, each having a surface to be exposed to the laser light beam, which is emitted from said laser light source of each said optical systems, to form an electrostatic latent image on the surface of the photosensitive body according to said image signal for each said color,
• each of said optical systems further including a rotary polygon mirror for scanning over the surface of said photosensitive body in a main scanning direction by deflecting the laser beam from said laser light source of each said optical system, and an f .theta. lens for fostering uniform-velocity scanning of the laser beam deflected by said rotary polygon mirror in the main scanning direction on each said photosensitive body;
• a storage unit for storing uniform velocity correction data, which is previously created for each mirror surface of said rotary polygon mirror, for correcting a possible expansion or contraction distortion of said electrostatic latent image in the main scanning direction on each said photosensitive body due to at least a positional error of characteristic errors of each said optical systems including said f .theta. lens;
• and
• an image clock generating unit for generating, upon receipt of said uniform velocity correction data regarding each mirror surface of the individual rotary polygon mirror from said storage unit, which mirror surface is used at a scanning time, an image clock pulse having a period corresponding to said uniform velocity correction data.