Patent ID: 7351950

Claim:
An optical beam scanning device, comprising a plurality of optical elements that are arranged on a housing and give a plurality of scanning lines to a plurality of photoconductor drums with an interval L, wherein when linear expansion coefficients of the housing, a frame for locating the photoconductor drums and a shaft, which is used for driving a belt or a recording medium carried on the belt on which images developed on the photoconductor are overlapped, are designated by αH, αF and αS, respectively, and when an interval between light beams positions on surfaces to be scanned in a sub-scanning direction as an optical path reflection is expanded by mirrors from a deflecting surface to the surfaces to be scanned is designated by BP, optical characteristics are designed so that intervals of the beams in the sub-scanning direction are shifted only by −(αH−2×αF+αS)×L+αH×BP per unit temperature.