To provide a light beam scanner in which the lifetime of a light emitting point can be prolonged by reducing the emission load of a light emitting point performing image formation.

In a multibeam light source having a plurality of light emitting points capable of independent modulation, and a light beam scanner scanning the surface of a photosensitive body by deflecting a light beam, a plurality of light emitting points for forming an image by scanning the surface of the photosensitive body, and one or more light emitting points for detection performing at least one of generation of a scan reference signal and correction of quantity of light are provided, and at least one of modulation of the light emitting point for image formation and correction of quantity of light is performed based on the scan reference signal generated from the light emitting point for detection or the quantity of light correction data.