A water-vapor generating apparatus used for reforming a hydrocarbon fuel is disclosed. The water-vapor generating apparatus includes a chamber body; a partitioning member to divide a space defined in the chamber body into a water-vapor discharge space and a heating space; a tubular pipe having a first opened end in water-communication with an external water-supply apparatus and a second opened end in vapor-communication with the water-vapor discharge space, wherein the tubular pipe extends through the heating space; and a heater configured to supply thermal energy to the heating space. Such a water-vapor generating apparatus may supply water-vapor, in a stable and uniform manner, to a fuel reforming apparatus.