A light beam scanning device scans a luminous flux irradiated from a light source and deflected by a deflector to a scanned surface through an optical system having a set of mirrors. A apparatus, such as the light beam scanning device, further includes a scanning line curve adjusting device to bend a first mirror of the set of mirrors so as to correct a curve in a scanning line on the scanned surface, and a scanning line tilt adjusting device to change orientation of a second mirror of the set of mirrors so as to correct a tilt in the scanning line on the scanned surface. The light beam scanning device may be provided in an image forming apparatus.