An optical scanning apparatus comprising: an optical deflector comprising: a mirror part that has a flat reflection surface and a grooved reflection surface , each of the flat reflection surface and the grooved reflection surface reflecting an incident light; and a first actuator that is adapted to reciprocally turn the mirror part about a first rotation axis , wherein the grooved reflection surface has a plurality of longitudinal grooves that extends parallel to the first rotation axis , and wherein each longitudinal groove has a facing inclination surface that is parallel to the first rotation axis and that has at least an opening-side portion of a facing inclination surface of a V-groove, an optical source that is configured to generate the incident light, the incident light entering the mirror part ; and an optical sensor disposed in a direction of a same angle as an absolute value of an emission angle of a two-time reflected light (L2), wherein the optical scanning apparatus is configured such that the two-time reflected light (L2) being emitted after the incident light (La) is reflected in each of the longitudinal grooves of the grooved reflection surface of the mirror part two times by the facing inclination surface ; wherein the absolute value of the emission angle of the two-time reflected light (L2) is constant regardless of a deflection angle (θ) of the mirror part about the first rotation axis , and wherein a light which is the incident light (La) being reflected by the flat reflection surface of the mirror part is a scanning light (Lb), and the two-time reflected light (L2) is a detection light of the optical sensor . an optical deflector comprising: a mirror part that has a flat reflection surface and a grooved reflection surface , each of the flat reflection surface and the grooved reflection surface reflecting an incident light; and a first actuator that is adapted to reciprocally turn the mirror part about a first rotation axis , wherein the grooved reflection surface has a plurality of longitudinal grooves that extends parallel to the first rotation axis , and wherein each longitudinal groove has a facing inclination surface that is parallel to the first rotation axis and that has at least an opening-side portion of a facing inclination surface of a V-groove, a mirror part that has a flat reflection surface and a grooved reflection surface , each of the flat reflection surface and the grooved reflection surface reflecting an incident light; and a first actuator that is adapted to reciprocally turn the mirror part about a first rotation axis , wherein the grooved reflection surface has a plurality of longitudinal grooves that extends parallel to the first rotation axis , and wherein each longitudinal groove has a facing inclination surface that is parallel to the first rotation axis and that has at least an opening-side portion of a facing inclination surface of a V-groove, an optical source that is configured to generate the incident light, the incident light entering the mirror part ; and an optical sensor disposed in a direction of a same angle as an absolute value of an emission angle of a two-time reflected light (L2), wherein the optical scanning apparatus is configured such that the two-time reflected light (L2) being emitted after the incident light (La) is reflected in each of the longitudinal grooves of the grooved reflection surface of the mirror part two times by the facing inclination surface ; wherein the absolute value of the emission angle of the two-time reflected light (L2) is constant regardless of a deflection angle (θ) of the mirror part about the first rotation axis , and wherein a light which is the incident light (La) being reflected by the flat reflection surface of the mirror part is a scanning light (Lb), and the two-time reflected light (L2) is a detection light of the optical sensor . <EOS>