An indicator includes a case mountable in a gas filling passage of a pressure container; a valve element which is urged toward one side of the case connectable to the pressure container, the valve element being movable in the case to a position balanced with gas pressure in the pressure container; a seal member for ensuring gas tightness between the valve element and the case; and an indicating member slidable relative to the case between a position protruding outside the case and a position not protruding. The spring force and a gas pressure force may be equally balanced at first and second balanced positions of the valve element.