To provide a tandem laser scanner which is small in the number of components of optical systems before a deflector.

The laser scanner is provided with a plurality of laser diodes, a plurality of collimator lenses and a beam synthesizing mirror as the optical systems before the deflector and aligns the optical paths relating to a horizontal scanning direction by the beam synthesizing mirror after discretely collimating the laser beams from the respective laser diodes to parallel light beams by the collimator lenses. The beam synthesizing mirror is provided with a plurality of reflecting surfaces for discretely reflecting the laser beams from the collimator lenses and the respective reflecting surfaces are provided with power in a vertical scanning direction, thereby, the beam synthesizing mirror is acted as a cylindrical lens as well.