Abstract: A focus adjusting device for a binocular which is constructed with a pair of object lens barrels, a pair of ocular lens barrels slidably fitted in the objective lens barrels, brackets for connecting the pairs of the object lens barrels and the ocular lens barrels, a hollow cylindrical shaft, on which the brackets are centrally hinged, a back-and-forth moving shaft inserted concentrically into the hollow cylindrical shaft, a seat member in a semi-circular shape, through which the outer peripheral surface of the hollow cylindrical shaft pierces, the seat member having a flattened platform, a finger plate member slidably fitted on the top flattened platform of the seat member to move left and right directions, each of the cylindrical shaft, the back-and-forth moving shaft, and the finger plate member having a long hole, through which a single pin studded upright from the back-and-forth moving shaft passes, the long hole in the finger plate member being formed slantly so that when the finger plate member is moved