Optical scanning device which detects a deflection angle of a mirror unit based on outputs from light detectors

An optical scanning device comprising:

• a light source which emits light;
• a light deflector having a mirror unit which includes:
• on a front surface side, a flat reflection part that emits incident light entering from the light source as scanning reflection light, and a groove-shaped reflection part having a longitudinal groove that extends in a predetermined direction and has a pair of inclined surfaces facing each other such that a groove width decreases from the front surface side to a back surface side, and which reflects the incident light a total of twice, once on each inclined surface and emits the reflected incident light as index light;
• and a first actuator that rotates the mirror unit in a reciprocating manner about a first rotation axis parallel to an extending direction of the longitudinal groove;
• a light detection unit which is disposed on a scanning trajectory of a scanning light spot of the scanning reflection light and at a light reception position of an index light spot of the index light, and is divided into a first light detector and a second light detector by a division line that divides the index light spot in a scanning direction of the scanning reflection light;
• and
• a deflection angle detection unit which detects a first deflection angle as a deflection angle of the mirror unit about the first rotation axis based on comparison between an output of the first light detector and an output of the second light detector.