An illuminating optical system comprises a truncated polyhedral pyramid (17) with oblique reflective surfaces (18) located at the center. Three concentric circles with radii (R1, R2, R3) (R1 < R2 < R3) share the center (P). Individual lenses (8) are arranged on intersections of the circle with the radius (R1) and straight lines radially extending through the center (P) at central angles (±) that equally divide a circumference. Light incidence lenses (9) are arranged such that the apexes of the light incidence lenses (9) locate on intersections of the circle with the radius (R2) and bisectors (central angles ²) of the central angles (±). LEDs (12) are mounted such that the apexes of the LEDs (12) locate on intersections of the circle with the radius (R3) and radial extensions of straight lines that connect the center (P) with the positions of the apexes of the light incidence lenses (9).
