Displaying optical system

A displaying optical system, comprising:

• a scanning member for deflecting a light emitted from a light source;
• a scanned surface on which an image is formed by scanning with the light deflected by the scanning member, the scanned surface being a reflection surface;
• an optical surface provided at a position common to a first optical path through which a light reflected by the scanned surface travels and a second optical path through which a light from the scanning member to the scanned surface travels, the optical surface, in accordance with a polarization direction, transmitting the light traveling through one of the first optical path and the second optical path and reflecting the light traveling through the other optical path;
• and
• a phase plate that emits a light which has been incident into the phase plate by changing a state of polarization of the incident light, the phase plate being provided at the position common to the first optical path and the second optical path.