Abstract: A color registration adjusting method in an image forming apparatus includes the steps of determining whether the detected pulse width for the edge of a photoreceptor belt is smaller than the expected pulse width thereof. If the detected pulse width is smaller than the expected pulse width, then the detected pulse width is set as a scanning start signal (an edge signal mixed) and a value obtained by subtracting a predetermined value from the currently expected pulse width is set as the next expected pulse width. Alternatively, if the detected pulse width is greater than or equal to the expected pulse width in the first step, the expected pulse width is set as the scanning start signal and a determination is made whether the counted value of a pulse is smaller than an offset value. If the pulse counted value is smaller than the offset value in the step, a value obtained by subtracting a predetermined value from the currently expected pulse width is set as the next expected pulse width.