An optical beam scanning device includes plural light sources, a pre-deflection optical unit, a light deflection unit, a post-deflection optical unit, and a horizontal synchronization unit. One of the formed plural latent images is formed by plural light beams while the other latent images are respectively formed by one light beam, and the light deflection unit deflects the light beams forming the plurality latent images by one surface or integrally processed surface thereof. The horizontal synchronization unit is on a position of an upstream side of scanning lines forming the latent image formed by the plural light beams and detects that the light beam forming the latent image formed by the plural light beams reaches a predetermined position. The image forming apparatus employs the optical beam scanning device and controls timing to form images by the respective light beams with reference to a moment when the light beam to be detected reaches a predetermined position.