An optical element that realizes light path conversion of transmitting light at low loss, allows easy incorporation of functions such as light convergence or the like, and can be easily made into a compact size includes upper and lower main surfaces of a light path converting element of a plane shape are facing each other, and a light incoming surface and a light outgoing surface are adjacent surfaces at about 90 degrees. A curved light path converting surface is formed so as to face the light incoming surface and the light outgoing surface. Light coming in from the light incoming surface repeats full reflection between the upper main surface and the lower main surface and goes on, and is reflected by the light path converting surface, thereby the light path thereof is converted, and light is ejected from the light outgoing surface.