A display optical system is disclosed which can attain a reduction in size and widening of an angle of view. The display optical system comprises an optical system including a first optical system and a second optical system. The first optical system includes a first surface decentered with respect to a central principal ray, and a second surface which reflects again light reflected on the first surface to the first surface. The first surface reflects the central principal ray incident on the first surface again from the second surface substantially to the opposite side to the previous reflection with respect to a normal on a hit point of the central principal ray. The first optical system directs light to an eye of an observer. The second optical system directs the illumination light to the image forming element and directs the display light to the first optical system.