An optical scanning device includes an optical scanning element which has a reflection mirror and is configured to perform reciprocating scanning of an optical flux radiated from a light source by resonance oscillations of the reflection mirror; a photo detector which is arranged at a position which a portion of the optical flux scanned by the optical scanning element in a reciprocating manner passes in both outgoing-path scanning and incoming-path scanning, and is configured to output a pulse signal having a predetermined width at a point of time that the scanned optical flux is detected; and the reference signal generator which is configured to detect timing between rising edge timing of one pulse signal and falling edge timing of the other pulse signal out of two pulse signals continuously outputted from the photo detector, and to generate the reference signal based on intermediate timing between the edge timings.