the clock signal outputted by frequency divider 82 this is because the clock signal outputted by the frequency divider 82 is further frequency divided by the flip flop 84 one cycle of the clock pulse of the image forming clock f out2 is equivalent to two cycles of the clock signal outputted by the frequency divider 82 the first pulse is gained by the frequency division with the factor 34 20 34 while the latter is gained with the factor 34 19 34 or 34 21 34 consequently the wavelength of the output clock signal f out2 changes by one pulse with respect to 40 pulses of the clock signal f out1 in other words the size of a correction dot is larger or smaller than that of a standard dot by m 40 u03bcm u00b1 0 25 u03bcm accordingly in order to obtain a predetermined changed magnification the number of correction dots indicated by the below equation are mixed in l 65000 dots equ3 the interval for mixing each correction dot is indicated as below in other words the below indicated number of standard dots exist for each interval it is assumed that the correction dots are mixed with the standard ones evenly during main scanning more specifically recording.