Optical scanning apparatus and image forming apparatus

An image forming apparatus for forming an image on a sheet, comprising:

• a first photosensitive member;
• a second photosensitive member;
• an optical scanning unit configured to scan said first photosensitive member and said second photosensitive member with first laser light and second laser light, respectively, depending on image information;
• first and second developing units configured to position electrostatic latent images, formed on said first and second photosensitive members by said optical scanning unit, with toner;
• and
• a transfer unit configured to transfer first and second toner images formed by developing the electrostatic latent images by said first and second developing units,
• wherein said optical scanning unit includes:
• a first light source;
• a second light source;
• a rotatable polygonal mirror configured to reflect and deflect first laser light emitted from said first light source and second laser light emitted from said second light source, said rotatable polygonal mirror reflecting the second laser light in a direction opposite to a reflection direction of the first laser light;
• a motor configured to rotationally drive said rotatable polygonal mirror;
• a first mirror configured to reflect the first laser light deflected by said rotatable polygonal mirror and configured to guide the reflected first laser light to said first photosensitive member;
• a second mirror configured to reflect the second laser light deflected by said rotatable polygonal mirror and configured to guide the reflected second laser light to said second photosensitive member;
• a first lens configured to image the first laser light deflected by said rotatable polygonal mirror on said first photosensitive member;
• a second lens configured to image the second laser light deflected by said rotatable polygonal mirror on said second photosensitive member;
• and
• a casing accommodating said rotatable polygonal mirror, said motor, said first and second mirrors and said first and second lenses, wherein said casing includes an accommodating portion including a top wall on which said motor is mounted, a first side wall opposing one end portion of said first lens with respect to a longitudinal direction of said first lens, a second side wall opposing the other end portion of said first lens with respect to the longitudinal direction, and an opening, and includes a cover portion configured to cover said opening, of said accommodating portion, provided at a position opposing a motor mounting surface of said top wall,
• wherein in a mounting range of said top wall of said accommodating portion in which said motor, said first and second mirrors and said first and second lenses are mounted with respect to a perpendicular direction perpendicular to both a rotational axis direction of said motor and the longitudinal direction of said first lens, at least one curved portion having a shape such that a part of said top wall projects so that said mounting surface approaches said opening is provided,
• wherein with respect to the longitudinal direction of said first lens, said curved portion has a length equal to a gap between said first side wall and said second side wall,
• wherein said top wall includes a recess on a surface opposite from said mounting surface at a portion corresponding to said curved portion,
• wherein said cover includes a first portion through which the first laser light passes and a second portion through which the second laser light passes, and
• wherein with respect to the rotational axis direction, a top end portion of said curved portion on an opening side of said casing, a reflecting surface of said rotatable polygonal mirror, and the first and second portions of said cover, are arranged in this order.