An optical scanning device is provided. The optical scanning device
comprises a light source, a deflection mirror reflectively deflecting a
light beam projected from the light source by performing a sine-wave
oscillation, a scanning optical element causing the light beam
reflectively deflected by the deflection mirror to scan a scanned surface
at a substantially constant velocity, wherein the following conditional
expression is fulfilled: 0.4<.phi.max/.phi.0<0.9/[(20/.phi.0)
(1/4)]. In this conditional expression, .phi.0 is an amplitude angle of
the sine-wave oscillation of the deflection mirror, and .phi.max is a
maximum rotational angle of the deflection mirror corresponding to an
effective write width.
