To provide an optical scanner which can be made small in size and can be easily adjusted at manufacturing.

As for an optical scanner 200, four optical scanning units 201A to 201D are installed, the units 201A to 201D are composed of a light source part for emitting a luminous flux, a scanning inputting optical system for guiding the luminous flux emitted from the light source part to a deflector, a deflector for deflecting the luminous flux so as to scan with the flux, a scanning image forming optical system for condensing the luminous flux deflected by the deflector on a surface to be scanned as a beam spot are used, and one surface to be scanned is continuously scanned by cooperatively actuating the respective optical scanning units 201A to 201D. Respective scanning/image forming optical systems 18A to 18D among two adjacent optical scanning units 201A to 201D are provided with at least one lens 70 in common.