An intermediate image is formed inside a first prism, and an image light, which is reflected on the order of a third surface, a first surface and a second surface, is transmitted through the first surface and reaches the eyes of the observer, therefore it is possible to make the entire optical system small and light in weight by making the first prism thin, and realize a high performance display device with a wide angle of view. Further, when an external light is passed through, for example, the first surface and the third surface and observed, a diopter scale is set to approximately zero, and thereby reducing the defocus or distortion of the external light when observed in a see-through manner. And, it is possible such that the shape of the first prism conforms to the face of the observer, the center is also close to the face.