Optical scanning device, image display device, and vehicle

An optical scanning device, comprising:

• a light source configured to emit a light beam;
• a light deflector configured to two-dimensionally deflect the light beam in a main scanning direction and a sub-scanning direction orthogonal to the main scanning direction;
• and
• an image former configured to form an image by two-dimensional scanning of the light beam performed by the light deflector, wherein
• a flat plate configured to transmit light incident on the light deflector and deflected reflection light from the light deflector, is arranged in an optical path of the light beam between the light deflector and the image former, and
• in a cross section in the sub-scanning direction, the flat plate is inclined in a direction in which an angle increases, the angle being formed by a virtual line, which forms a smaller angle with a perpendicular line of the flat surface, of two virtual lines each of which diagonally connects an end of the flat plate and an end of the image former, and the perpendicular line of the flat surface.