An optical scanning device includes a light source, a light deflector for deflecting and scanning a light beam from the light source, a scanning imaging optical system for imaging the light beam via the light deflector onto a scanned face, a light beam detecting device for detecting a position of the light beam, a separation optical system provided in the light beam detecting device for separating the light beam into a plurality of separation light beams in a sub-scanning direction, a plurality of light detectors provided in the light beam detecting device to be disposed in different positions in the sub-scanning direction, and a plurality of light receiving sections provided in the light detectors, respectively, at least one light receiving section provided in the light detector being disposed such that the end portion on a side for detecting the separation light beam has a predetermined angle to the end portion of the other light detector.