<p>A projection optical system is described. A first optical part (1) comprises at least one optical lens, and projects and displays light beams. A second optical part (2) comprises an image forming element (6) and at least one optical lens, and emits incident light beams as light beams with images. A third optical part (3) comprises a light source unit (5) and a deflector (4) that is located between the first and second optical parts (1, 2), and directs light beams emitted from the light source unit (5) to the second optical part (2) and directs the light beams with images emitted from the second optical part (2) to the first optical part (1).</p>
