A scanning optical system suitable for use in a light projecting and receiving apparatus suitable for detecting objects, wherein the scanning optical system is a laser radar system comprising: a mirror unit (MU) comprising a first mirror surface (M1) and a second mirror surface (M2) inclined to each other, and each of which inclines to a rotation axis (RO); and a light projecting system (LPS) including at least one light source (LD) to emit a light flux (LB) toward the first mirror surface (M1), wherein the light flux (LB) emitted from the light source (LD) is reflected on the first mirror surface (M1) of the mirror unit (MU), thereafter, reflected on the second mirror surface (M2), and then, projected so as to scan in a main scanning direction onto an object in accordance with rotation of the mirror unit (MU), and wherein in a case where a virtual plane (VP) is set in a range including the object, the light flux (LB) reflected on the second mirror surface (M2) has, upon entering the virtual plane (VP) as a spot light (SL), a cross sectional shape in which a length in a direction orthogonal to the main scanning direction is longer than a length in the main scanning direction, wherein the mirror unit (MU) includes a plurality of pairs of the first mirror surface (M1) and the second mirror surface (M2), and an intersection angle between the first mirror surface (M1) and the second mirror surface (M2) in each pair is different from respective intersection angles of the other pairs, characterized in that the laser radar system is configured such that said light flux (LB) forms spot lights (SL) in the virtual plane (VP) that are arranged side by side in the sub-scanning direction and made to come in contact with each other or superimposed on each other. a mirror unit (MU) comprising a first mirror surface (M1) and a second mirror surface (M2) inclined to each other, and each of which inclines to a rotation axis (RO); and a light projecting system (LPS) including at least one light source (LD) to emit a light flux (LB) toward the first mirror surface (M1), wherein the light flux (LB) emitted from the light source (LD) is reflected on the first mirror surface (M1) of the mirror unit (MU), thereafter, reflected on the second mirror surface (M2), and then, projected so as to scan in a main scanning direction onto an object in accordance with rotation of the mirror unit (MU), and wherein in a case where a virtual plane (VP) is set in a range including the object, the light flux (LB) reflected on the second mirror surface (M2) has, upon entering the virtual plane (VP) as a spot light (SL), a cross sectional shape in which a length in a direction orthogonal to the main scanning direction is longer than a length in the main scanning direction, wherein the mirror unit (MU) includes a plurality of pairs of the first mirror surface (M1) and the second mirror surface (M2), and an intersection angle between the first mirror surface (M1) and the second mirror surface (M2) in each pair is different from respective intersection angles of the other pairs, characterized in that the laser radar system is configured such that said light flux (LB) forms spot lights (SL) in the virtual plane (VP) that are arranged side by side in the sub-scanning direction and made to come in contact with each other or superimposed on each other. <EOS>