A scanning optical apparatus uses a light source pair that includes at least two light sources to scan a same scan line. The scanning optical apparatus includes: a first group of light sources which include a first light source of a light source pair and are lined up on a first line; and a second group of light sources which include a second light source of the light source pair and are lined up on a second line. The first line and the second line are inclined with respect to reference lines corresponding to scan lines so that the first light source and the second light source of the light source pair scan the same scan line. Moreover, a distance between the first light source and the second light source of the light source pair is at least twice a distance between two adjacent light sources in the first line.