NOVELTY - A heated fluid flow path assembly (70) has fuel flow path (90) and flow path (60) for combustion gas which vaporizes the fuel by heat exchange. A controller (24) corrects spray amount of cooling water from a sprayer (62) to the flow path assembly, based on the temperature distribution along the air flow direction in the flow path assembly using temperature sensors (71,72).    USE - For evaporating fuel such as methanol, so as modify into hydrogen rich gas used by fuel cell of electric vehicle.    ADVANTAGE - Due to spray of cooling water, overheating of the fuel evaporator is prevented and stabilized running state with uniform temperature distribution is achieved.    DETAILED DESCRIPTION - The temperature sensors measures at two places along upstream and downstream of combustion gas passing through the corresponding flow path. The controller corrects the spray amount of the cooling water based on the temperature difference measured by the sensors and the sensor (73) arrange at the outlet. The flow path assembly is connected to an injector (63) which sprays combustion fuel to combustion air and generates mixed gas. A combustion mechanism carries out the catalyzed combustion of the mixed gas and generates the combustion gas. A condenser (65) condenses and liquefies the moisture content in the air flow of the fluid path assembly. A pump (67) recirculates the liquefied moisture content into the spraying unit. A modifier modifies the fuel vaporized with the fuel evaporator to hydrogen rich gas. An electric vehicle is equipped with a fuel cell which receives heated gas from modifier and performs power generation required for vehicle drive. INDEPENDENT CLAIMS are also included for the following:    (1) computer program;    (2) computer readable recording medium: and    (3) electric motor vehicle with fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the fuel evaporator. (Drawing includes non-English language text).    controller (24)    flow path assembly (60)    air pump (61)    injectors (62,63)    condenser (65)    water pump (67)    flow path assembly (70)    temperature sensors (71,72,73)