NOVELTY - A evaporation section (56) generates water vapor and supplies to a modification section (21). One end of a drain pipe (57) is connected to the water inlet of the evaporation section. A drain valve (58) of the drain pipe is closed valve during driving operation of fuel cell system, and the drain valve is opened when driving operation of fuel cell system is stopped.    USE - For stopping of fuel cell system (claimed).    ADVANTAGE - Since the water does not remain in the modifier, due to the water drain pipe, after the shutdown of the fuel cell system, even if the atmospheric temperature of the system serves as freezing point, the freezing of water in the modifier is prevented and damage of the freezer by the freezing is prevented. Excess warming-up time to dissolve the ice when starting the fuel cell system is reduced. Therefore starting time of the fuel cell system is reduced even in winter.    DETAILED DESCRIPTION - The water collected in the evaporation section is collected through the drain pipe, when the fuel cell system is stopped.    INDEPENDENT CLAIMS are also included for the following:    (1) restarting method of fuel cell system involves supplying preset amount of water to the modifier before starting of the modifier, when the drive operation of the fuel cell system is restarted; and    (2) fuel cell which has controller to control the opening-closing of valve attached to the water drain pipe and with the modifier. A reaction zone (22) of the modifier decreases the carbon monoxide in the reformed gas from the modification zone (21) and a selective oxidation zone (23) further decreases the carbon monoxide in the reformed gas supplied form the reaction zone. One end of the drain pipe is connected to reservoir tank which is arranged at the lower position of the storage tank.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic view of the fuel cell system.(Drawing includes non-English language text).    modifier (20)    modification zone (21)    reaction zone (22)    selective oxidation zone (23)    evaporation section (56)    drain pipe (57)    drain valve (58)