A propellant filling device for filling a propellant into an aerosol container containing a liquid concentrate and the propellant previously filled thereinto includes a valve opening member that continuously presses a valve member to open a valve system of the aerosol container and has a communicating hole. On the upper end side of the valve opening member, a flow conduit is provided. A valve member is provided in the flow conduit to allow a flow channel of the flow conduit to be closed. The valve system is kept in an open state, and when the pressure in the aerosol container is higher than the supply unit side pressure, the backflow of aerosol content is prevented, and when the supply unit side pressure is higher than the pressure in the aerosol container, the propellant flows into the aerosol container.