Optical device and head-mounted display using said optical device

The present invention is directed to provide a thin and light optical device for observing visual information with a large angle of visual field and a head-mount display (HMD) using said optical device. An optical device according to the present invention comprises a refracting means consisting of a refracting element (1a, 1b, 1c, 1d, 1e, 1f, 1l, 1t) with half-mirror coating (2a, 2b, 2c, 2e, 2f, 2t) and a circularly polarized light selecting semitransparent mirror (3a, 3c, 6b, 6e, 6f, 6t), which are disposed in the described order from the incident side. The circularly polarized light selecting semitransparent mirror (3a, 3c, 6b, 6e, 6f, 6t) consists of a quarter-wave plate (5), a half-mirror (2) and a polarizer (4) or cholesteric liquid crystal (6b, 6e, 6f, 6t), which are disposed in the described order from the incident side. A thin and high-magnification optical system is obtained by using the circularly polarized light selecting semitransparent mirror (3a, 3c, 6b, 6e, 6f, 6t) that first reflects incident light (Li) in a clockwise circularly polarized fashion and allows the counterclockwise circularly polarized light having made 1.5 round trips to pass without being reflected. A head-mount display (HMD) according to the present invention includes a liquid crystal display (LCD) (9c, 9d, 9l, 9n), a back light (8c, 8d, 8l, 8n) for the LCD and the above-mentioned optical device for magnifying an image of the LCD.