An optical scanning device comprising: a scanning member configured to scan incident laser beams in a predetermined main scanning direction; a plurality of light sources (611A-614A) configured to emit the laser beams respectively from positions that are different along a sub scanning direction that is perpendicular to an optical axis direction of the laser beams and the main scanning direction; a first reflection mirror inclined with respect to the optical axis around the main scanning direction as a rotation axis, inclined with respect to the optical axis around the sub scanning direction as another rotation axis, and configured to reflect the laser beams emitted from the light sources (611A-614A); and a second reflection mirror inclined with respect to the optical axis around the main scanning direction as a rotation axis, inclined with respect to the optical axis around the sub scanning direction as another rotation axis, and configured to reflect the laser beams reflected by the first reflection mirror toward the scanning member, the optical scanning device further comprising: an aperture having an opening portion; and a first blocking member configured to block a part of the laser beams; characterized in that the aperture is disposed in a state where a longitudinal direction of the opening portion is inclined by a predetermined angle around the optical axis direction of the laser beams as a rotation axis with respect to the main scanning direction, the opening portion being configured to restrict a beam path width of the laser beams that are emitted from the light sources (611A-614A) and incident on the first reflection mirror, wherein the aperture includes a first cut portion which is formed at a predetermined position of the opening portion to extend in a direction perpendicular to the longitudinal direction of the opening portion, and in which first cut portion said first blocking member can be inserted. a scanning member configured to scan incident laser beams in a predetermined main scanning direction; a plurality of light sources (611A-614A) configured to emit the laser beams respectively from positions that are different along a sub scanning direction that is perpendicular to an optical axis direction of the laser beams and the main scanning direction; a first reflection mirror inclined with respect to the optical axis around the main scanning direction as a rotation axis, inclined with respect to the optical axis around the sub scanning direction as another rotation axis, and configured to reflect the laser beams emitted from the light sources (611A-614A); and a second reflection mirror inclined with respect to the optical axis around the main scanning direction as a rotation axis, inclined with respect to the optical axis around the sub scanning direction as another rotation axis, and configured to reflect the laser beams reflected by the first reflection mirror toward the scanning member, the optical scanning device further comprising: an aperture having an opening portion; and a first blocking member configured to block a part of the laser beams; an aperture having an opening portion; and a first blocking member configured to block a part of the laser beams;