Abstract: A binocular comprising a bedplate provided with a pair of left and right objective lenses, a support frame standing on the bedplate, and a casing detachably attached to the bedplate in such a manner to cover the support frame. All of the optical members except the objective lenses are mounted on the support frame so that each of the optical members may easily be inspected and adjusted by removing the casing. The interval between the left eyepiece and the right eyepiece may be adjusted to the interval of the user's own eyes by moving one of the eyepiece members on either side, wherefore rectangularly shaped objective lenses which are deemed to be most suitable from a human engineering point of view to the visual angle of a human being's eyes to obtain a clean and wide view can be utilized.