A propellant filling device for filling a propellant into an aerosol container, which contains a liquid concentrate and the propellant previously filled thereinto, through a valve system provided in the aerosol container, comprising: a valve opening member provided in a lower end portion thereof so as to face the valve system of the aerosol container to continuously press a valve member (6, 44) of the valve system to open the valve system; a communicating hole provided in the valve opening member so as to be able to communicate with an inside of the aerosol container when the valve system is opened; a flow conduit provided on an upper end side of the valve opening member so as to communicate with a propellant supply unit through a supply channel; a valve member provided in the flow conduit to allow, when the propellant flows under pressure from the supply unit to the aerosol container, a flow channel of the flow conduit to be opened by a pressure of the propellant and to allow, when the propellant flows under pressure from the aerosol container to a supply unit side, the flow channel of the flow conduit to be closed by a pressure in the aerosol container; and a small flow conduit provided in the flow conduit in such a manner that a gap is provided between an inner peripheral surface of the flow conduit and the small flow conduit to allow the flow channel of the flow conduit and the communicating hole of the valve opening member to communicate with each other through the small flow conduit; wherein the small flow conduit has a communicating port provided in its side wall so as to communicate with the flow channel and a distal opening covered with the valve member; and wherein, during filling of the propellant from the supply unit into the aerosol container, the valve system of the aerosol container is kept in an open state by continuously pressing the valve member (6, 44) of the aerosol container by the valve opening member, and in this open state, when the aerosol container side pressure is higher than the supply unit side pressure, the valve member comes, by the aerosol container side pressure, into contact with a valve seat provided on an inner surface of the flow conduit to allow the flow channel of the flow conduit to be closed to prevent backflow of the propellant and the aerosol content to the supply unit side, and on the other hand, when the supply unit side pressure is higher than the aerosol container side pressure, the valve member is moved to a small flow conduit side by a pressure of the propellant supplied from the supply unit so that a propellant communication channel is formed between the inner peripheral surface of the flow conduit and the valve member to allow the propellant supplied from the supply unit to flow to an aerosol container side through the valve member and the communicating port. a valve opening member provided in a lower end portion thereof so as to face the valve system of the aerosol container to continuously press a valve member (6, 44) of the valve system to open the valve system; a communicating hole provided in the valve opening member so as to be able to communicate with an inside of the aerosol container when the valve system is opened; a flow conduit provided on an upper end side of the valve opening member so as to communicate with a propellant supply unit through a supply channel; a valve member provided in the flow conduit to allow, when the propellant flows under pressure from the supply unit to the aerosol container, a flow channel of the flow conduit to be opened by a pressure of the propellant and to allow, when the propellant flows under pressure from the aerosol container to a supply unit side, the flow channel of the flow conduit to be closed by a pressure in the aerosol container; and a small flow conduit provided in the flow conduit in such a manner that a gap is provided between an inner peripheral surface of the flow conduit and the small flow conduit to allow the flow channel of the flow conduit and the communicating hole of the valve opening member to communicate with each other through the small flow conduit; wherein the small flow conduit has a communicating port provided in its side wall so as to communicate with the flow channel and a distal opening covered with the valve member; and wherein, during filling of the propellant from the supply unit into the aerosol container, the valve system of the aerosol container is kept in an open state by continuously pressing the valve member (6, 44) of the aerosol container by the valve opening member, and in this open state, when the aerosol container side pressure is higher than the supply unit side pressure, the valve member comes, by the aerosol container side pressure, into contact with a valve seat provided on an inner surface of the flow conduit to allow the flow channel of the flow conduit to be closed to prevent backflow of the propellant and the aerosol content to the supply unit side, and on the other hand, when the supply unit side pressure is higher than the aerosol container side pressure, the valve member is moved to a small flow conduit side by a pressure of the propellant supplied from the supply unit so that a propellant communication channel is formed between the inner peripheral surface of the flow conduit and the valve member to allow the propellant supplied from the supply unit to flow to an aerosol container side through the valve member and the communicating port.