An optical scanning device comprising: a light source (110, 120, and 130) to emit a light beam; a scanning member to deflect the light beam emitted from the light source (110, 120, and 130) to cause the deflected light beam to two-dimensionally scan a scanning area (G1) in a first direction and a second direction perpendicular to the first direction; and an incident optical system to guide the light beam emitted from the light source to the scanning member , the incident optical system including the light source (110, 120, and 130), wherein the scanning area (G1) includes an image-forming-area (G10) and a non-image-forming area (G11) surrounding the image-forming area (G10), wherein the non-image-forming area (G11) includes a non-detection area (G13, G14) and a first detection area (G12), wherein the non-detection area (G13, G14) is adjacent to the first detection area (G12) in the first direction, wherein the non-detection area (G13, G14) is adjacent to the image forming area (G10) in the second direction, further comprising a first sensor to detect a synchronization of deflecting and scanning of the scanning member wherein the first sensor is disposed in the first detection area (G12); and characterised in that at least one component of the incident optical system is disposed in the scanning optical path ranging from the light deflector to the non-detection area (G13, G14) and is not disposed in the scanning optical path ranging from the light deflector to the image-forming area (G10), and is not disposed in the scanning optical path ranging from the light deflector to the first detection area (G12). a light source (110, 120, and 130) to emit a light beam; a scanning member to deflect the light beam emitted from the light source (110, 120, and 130) to cause the deflected light beam to two-dimensionally scan a scanning area (G1) in a first direction and a second direction perpendicular to the first direction; and an incident optical system to guide the light beam emitted from the light source to the scanning member , the incident optical system including the light source (110, 120, and 130), wherein the scanning area (G1) includes an image-forming-area (G10) and a non-image-forming area (G11) surrounding the image-forming area (G10), wherein the non-image-forming area (G11) includes a non-detection area (G13, G14) and a first detection area (G12), wherein the non-detection area (G13, G14) is adjacent to the first detection area (G12) in the first direction, wherein the non-detection area (G13, G14) is adjacent to the image forming area (G10) in the second direction, further comprising a first sensor to detect a synchronization of deflecting and scanning of the scanning member wherein the first sensor is disposed in the first detection area (G12); and characterised in that at least one component of the incident optical system is disposed in the scanning optical path ranging from the light deflector to the non-detection area (G13, G14) and is not disposed in the scanning optical path ranging from the light deflector to the image-forming area (G10), and is not disposed in the scanning optical path ranging from the light deflector to the first detection area (G12). <EOS>