To provide a deflection scanning device, a scanning optical device, and image forming device, which have high accuracy, a long life, and high reliability, in which even if vibration or impact is suddenly applied to the deflection scanning device during rotation thereof, or the rotation driving time advances, leak of oil to the outside of a bearing is suppressed by generating a desired dynamic pressure to reduce the abrasion of the bearing by an insufficient oil film.

The deflection scanning device A comprises: a rotary polygon mirror 1 deflecting and scanning a luminous flux emitted from a semiconductor laser unit 29; and a rotating shaft 2 and a sleeve 3 for rotatably supporting the polygon mirror 1. The rotating shaft 2 and the sleeve 3 include: a pair of dynamic pressure generating grooves 2a and 2b on the rotating shaft 2 side; and cylindrical bearing forming parts 3a and 3b on the sleeve 3 side, and the dynamic pressure generating grooves are vertically asymmetric by extending at least one of the dynamic generating grooves axially upward or downward. The bearing forming parts 3a and 3b on the sleeve 3 side include extension parts L axially longer than the dynamic pressure generating grooves 2a and 2b.