Abstract: A prostascope with a bridge includes a guide member which has a guide surface for a laser beam emitting end of a fiber cable at the bottom thereof and which is attached to the tip of the bridge, a reflector which is formed with a slant reflecting surface having a predetermined angle of reflection and which is detachably attached to a mounting portion of the guide member such that the reflector is prevented from rotating relative to the guide member and that a threaded end of the tip of the bride penetrates the reflector, and a cap nut which is removably screwed onto the threaded end of the bridge.