OPTICAL SCANNING DEVICE, IMAGE DISPLAY DEVICE, HEADS-UP DISPLAY, AND MOBILE OBJECT

An optical scanning device, an image display device, a heads-up display, and a mobile object. The optical scanning device includes a light source configured to emit scanning light, a light quantity adjuster provided with a plurality of optical attenuators having different light transmittances, the light quantity adjuster configured to change a light-intensity of the scanning light by switching one of the plurality of optical attenuators placed on an optical path, by movement of the light quantity adjuster, to scan a to-be-scanned surface using the scanning light passed through the light quantity adjuster, and a home position sensor configured to detect that the light quantity adjuster is present at a predetermined position. The light source starts emitting the scanning light after one of the plurality of optical attenuators is placed on the optical path at a time of startup.