An optical scanner includes a single deflector to optically scan a plurality of target surfaces to be scanned. The deflector has a common rotary axis for deflecting reflective surfaces and is shared by all the beams from a plurality of light sources. The optical scanner includes photodetectors arranged to receive the beams deflected at the deflector. The beams traveling toward the deflector have an open angle in a deflecting rotation plane. A scanning optical system for guiding the deflected beam to the corresponding target surface includes two or more scanning lenses. A scanning lens proximate to the target surface passes only the beams traveling toward the same target surface. Scanning lenses proximate to the target surfaces for guiding the beams to different target surfaces have optical actions different from each other.