An image forming method and apparatus which forms an image by using PWM to properly reproduce tones at a low density in the image formation, and attain a high-quality image without reducing the resolution in the dot formation corresponding to a high density value. A color laser beam printer using the PWM to which the present invention is applied forms a latent image onto a photosensitive drum by the laser beam irradiated from a semiconductor laser. The waveform of a chopped wave signal used in the PWM is set to be unique with respect to each color component, and be asymmetrical to the center of each pixel represented by the image signal in synchronization with the waveform of the chopped signal. Accordingly, the interval of dots formed to correspond to each color component is relatively wide when the density value is small, while the interval is relatively narrow when the density value is large.