An ultra wide-angle high-resolution optical system includes, from a human-eye observation side to a side at an image display unit, a first, second, third, fourth, and fifth lenses sequentially and coaxially arranged in the direction of an optical axis. A relationship of the focal lengths of the first, second, third, fourth, and fifth lenses meet a certain criterion. In addition, the first lens, third lens, and fourth lens are positive lenses, and the second lens and fifth lens are negative lenses. At the same time, the relationship of refractive indexes of the first lens, second lens, third lens, fourth lens, and fifth lens at the line d and the Abbe numbers thereof meet a certain criterion. In this way, an image displayed on the display unit is magnified by the optical system and then imaged on the human-eye. Also disclosed is a head-mounted display apparatus including the optical system.