Abstract: Protective mask (1) comprising a frame (5) suitable for being mounted on the face of a user, a window (2) carried by said frame, an optical display system (10) which comprises a display (12) capable of projecting an image, and a prism (20) capable of receiving said image from said display and forwarding it, characterised in that the prism (20) has a first (21) and a second (22) active face and a basal face (23), the window having, on its inner face (3), a projection area (30), and said display and said prism are configured and arranged so that said display projects said image onto the first active face (21) of the prism (20), the image crosses the prism and is reflected by the basal face (23) of the prism (20) to the second active face (22), the image is projected from said second active face (22) of the prism (20) onto said reflection area (30) of said window (2), and said window projects said image into the eye of the user (41).