To form a good color image even when a divisional scanning line has fluctuation in a main scanning direction due to variation in the environment in the case where the image is formed by using a divisional scanning optical device for forming one scanning line from a plurality of divisional scanning lines.

When the color image is formed, positions of connection points between images formed by each divisional scanning line, i.e., the connection points of the images in the main scanning direction are varied by each of colors of Y, M, C and K. As a result, even when the positions of the divisional scanning lines are shifted by the variation of the environment such as a temperature and then the position shift in the main scanning direction occurs in the divisional image, the turbulence in the image becomes inconspicuous and forming of the good image can be performed without using an expensive and highly accurate position correction circuit.