photosensitive drums 1 a 1 b 1 c and 1 d in the image formation stations y m c and bk respectively with the predetermined control timing for the image formation sequence the yellow magenta cyan and black colors are the color components into which the optical image of an intended full color image is separated meanwhile the feed roller 18 of the sheet feeding portion 16 begins to be rotated with predetermined timing as a result the recording mediums s in the cassette 17 begin to be fed into the apparatus main assembly 100 while being separated one by one after being fed into the apparatus main assembly 100 each recording medium s is temporarily held by the pair of registration rollers 19 as the leading edge of the recording medium s comes into contact with the nip between the pair of registration rollers 19 which are not rotating when the recording medium s comes into contact with the nip then the pair of registration rollers 19 begins to be rotated in synchronism with the rotation of the transfer belt 11 and the formation of the toner image on the peripheral surface of the photosensitive drum 1 a d allowing thereby the recording medium s to be conveyed to the nip between the electrostatic adhesion roller 22 and transfer belt 11 and conveyed through the nip while the recording medium s is conveyed through the nip between the electrostatic adhesion roller 22 and transfer belt 11 the recording medium s is pressed onto the outward surface of the endless transfer belt 11 in addition while the recording medium s is conveyed through the nip between the adhesion roller 22 and transfer belt 11 voltage is applied between the transfer belt 11 and.