NOVELTY - Fuel reformer comprises a reforming unit (3) to which fuel for reforming in the fuel storage tank (6) is supplied, via a vaporizer (2). A control apparatus comprising a return valve (9), is provided to selectively return the vapors formed in evaporation unit to fuel storage tank, when excess fuel vapors are generated.    USE - To supply reformed gas to energy converter of fuel cell.    ADVANTAGE - The excess fuel vapors are returned to storage portion and cooled. The supply of excess fuel vapors for reforming and useless consumption of reformed fuel, can be prevented, thereby improving overall energy efficiency. This also prevents the pressure rise in fuel storage part. The overall amount of fuel for reforming is maintained to predetermined value. Thermal efficiency is improved as the recovered heat is used again. Quality of reformed gas is maintained satisfactorily. Abnormal situations like damage, rupture or destruction of reformer is prevented before hand.    DETAILED DESCRIPTION - This invention makes the reforming fuel such as hydrogen by the modification reaction of fuel such as methanol. Fuel reformer control apparatus comprises a detection unit which detects the deviation of the amount of fuel vapor currently formed, from a predetermined value, based on load of energy converter. A pressure detection unit detects the pressure of return flow path, which returns excess fuel vapor to fuel storage tank, and prevents the return of low pressure vapor to storage tank. A differential detection unit detects the difference in the amount of fuel vapor currently formed and the predetermined vapor quantity. The return valve is equipped with cooling unit to cool the reformed fuel vapor. The fuel in evaporation unit is heated to raise the temperature to a predetermined value. A controller is provided to start the supply of vapor to reforming portion. A supply control unit supplies fuel for reforming to the evaporation unit based on the load of energy convertor. A return valve returns at least one portion of the vaporized fuel to the fuel storage tank, when the pressure or temperature of fuel for reforming, detected by the sensors exceeds the predetermined value. A stop decision unit is provided to judge the stopping of drive of modifier. The returning of the fuel vapors to storage tank is continued until the pressure or temperature of vapor flow in flow path to reformer, is lower than predetermined value.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of fuel reformer. (Drawing contains non-English text).    Evaporation unit (2)    Reforming unit (3)    Fuel storage tank (6)    Return valve (9)