It is intended to provide an image forming apparatus and image forming method capable of partial magnification corrections on various partial variations of magnification as well as constant and uniform positional shift regardless of any sections. A modulated image clock of a reference color (black) is generated from a clock generated at an image clock generating section 23 and an address is generated at an address generating circuit 36 basing on the modulated image clock. Output sections 30 for respective colors other than the reference color read out correction coefficients from correction coefficient memories 15 of respective colors following the address generated. Frequency modulator circuits 31 modulate image clocks in accordance with correction coefficients. PWM 33 outputs a driving pulse to a laser driver 6 basing on modulated image clocks synchronized with a reference signal 40 by synchronizer circuits 32 and inputted image data.