An erecting prism of a binocular includes a first and a second prism, which are held by a holder, and the holder being supported vertically movable and laterally immobile with respect to a thin plate. The thin plate is supported laterally movable and vertically immobile with respect to a right moving body. A shaft reception means is provided, for rotatably supporting a jig, at the right eyepiece cylinder that is attached to the rear wall 303B of the right moving body. The position of erecting prism is adjusted by using a jig to move the holder vertically with respect to the thin plate, and to move the thin plate laterally with respect to the right moving body. The jig may be supported by the shaft reception means and rotated.