A scanning optical apparatus includes, for example, a light source that outputs a light beam that has been pulse width modulated in accordance with input image data and a deflection unit that deflects the light beam so that the light beam scans the surface of an image carrier in the main scanning direction. The scanning optical apparatus furthermore includes a correction unit that corrects the pulse width and light amount applied to the light beam at each scanning position in the main scanning direction on the image carrier in accordance with focus error in the light beam at each scanning position.