A fluid fuel mediator connectable to a fluid fuel server and/or a power generator includes a fluid fuel inlet and/or a fluid fuel outlet, a storage vessel having a storage material which storages a fluid fuel, and at least one of an information memory, an information indicator, and an information transmitter. Pieces of information to be stored, displayed, or transmitted include information on a necessary filled amount, information on the number of times of filling, information on a flow rate of the fluid fuel, information on a residual amount of the fluid fuel, and information on the kind of the storage material. The fuel gas mediator has a temperature control mechanism.