Patent attributes
An optical beam scanning device comprises optical beam scanning means for rotational polygonal mirror to deflect entering luminous flux and scan an object to be scanned with the luminous flux; pre-deflection optical system which shapes a luminous flux emitted from light source means to image the resultant luminous flux onto the optical beam scanning means; and imaging optical system which images the luminous flux from the optical beam scanning means onto the object to be scanned. In the optical beam scanning device, the imaging optical system comprises an imaging optical element that in the entire main scanning area for luminous flux from the optical beam scanning means, the central scanning position has a main scanning direction curvature different from that of the scanning position of the scanning end, and a scanning angle α0 [rad] at which the optical beam scanning means scans the object to be scanned with the luminous flux is defined by the following expression,α0≦π{(2/N)−(Vr/3)×10−7}wherein N indicates the number of surfaces of the rotational polygonal mirror and Vr [r.p.m.] indicates the revolution of the rotational polygonal mirror.