1. An image forming device comprising: reading means for reading an image on an original document in a main scanning direction and a sub-scanning direction orthogonal to the main scanning direction, the reading means having first and second line sensors for dividing data read in a main scanning region which corresponds to one line into two portions and simultaneously outputting divided data by individually assigning it to a plurality of channels, each of the first and second line sensors being adapted to sequentially output pixel data composing image data read in the main scanning direction, starting from pixel data of a pixel at one end in the main scanning direction; first converting means for rearranging pixels in image data that is assigned to the plurality of channels and simultaneously output from the reading means and outputting sequentially in the main scanning direction image data corresponding to the one line; second converting means for converting image data that is arranged in the main scanning direction and is supplied from the first converting means to simultaneously output pixel data corresponding to a plurality of pixels in the sub-scanning direction; image processing means, having a plurality of image processing sections that are arranged in parallel, for performing parallel image processing of the pixel data corresponding to the plurality of pixels that is simultaneously output from the second converting means and outputting image data corresponding to a plurality of lines; and image outputting means for simultaneously outputting a plurality of beams each corresponding to image data of one line of the plurality of lines output from the image processing means.