An optical device with less influence of stray light is provided. The optical device is thin and includes a half mirror, a first lens, a retardation plate, a reflective polarizing plate, and a second lens. In the optical device, a geometric phase lens which has negative and positive refractive power is used as the first lens, whereby images can be focused after magnified optically. Thus, the optical device can have a wide viewing angle. In the case where stray light occurs due to birefringence of an optical material, negative refractive power of the first lens can prevent the stray light from being focused on the eye direction. Accordingly, image degradation recognized due to stray light can be prevented.