1. An image forming apparatus with a plurality of colors, said apparatus comprising: an original table for placing thereon an original which possesses at least a first color and a second color; original scanning means for optically scanning an original placed on said original table, said means having an optical system to feed the image reflecting light coming from the original into a given light path; color component detection means for transmitting electric signals corresponding to said first and second colors in response to the image reflecting light, said means being movably provided on said light path on which said image reflecting light coming from said optical system of said original scanning means passes; original color identifying means for identifying different color areas from the electric signals for said first and second colors transmitted from said color component detection means and for storing the color and positional data for the first and second colors in different color areas; image forming means for forming an image of given colors of the original on an image forming medium by using said image reflecting light coming from said optical system of said original scanning means and by selectively driving a first and a second developing units which correspond to said first and second colors respectively; image erasing means for selectively erasing an image to be formed by said image forming means; image forming medium return means for selectively returning said image forming medium to said image forming means after formation of an image by said image forming means; first control means for producing a first control signal to drive said original scanning means and said color component detection means for a given number of times prior to actual formation of an image; second control means for reading out, at the time of the first image forming operation, said first color data that have been stored in said original color identifying means to send them to said first developing unit of said image forming means as drive signals and said second positional data which correspond to said second color data to send them to said image erasing means as erasure data and for producing a second control signal to said image forming medium return means as an instruction for a return operation; and third control means for reading out, at the time of the second image forming operation, said second color data that have been stored in said original color identifying means to send them to said second developing unit of said image forming means and said first positional data which correspond to said first color data to send them to said image erasing means as erasure signals.