A disclosed image forming apparatus includes a recording unit which records image data on a recording medium; a first spread spectrum clock generator receiving a first clock signal, providing the first clock signal with frequency diffusion to have a first predetermined frequency diffusion width, and outputting a second clock signal; a PLL circuit outputting a third clock signal synchronously oscillating at a frequency obtained by multiplying the frequency of the first clock signal; an image processing unit receiving the third clock signal, and outputting the processed image data in synchronism with the third clock signal; a speed conversion unit receiving the second and third clock signals, and receiving and outputting the image data in synchronism with the second clock signal; and an input and output control unit outputting the image data to the recording unit in synchronism with the second clock signal.