NOVELTY - A fuel reformer has reformation portion, modifier, raw material supplier, sensor and flow rate controller. The controller adjusts the flow rate allocation of a heat exchange flow path which passes through a heat exchanger and results in a supply port of the modifier. The controller adjusts the flow rate allocation of the heat exchange and bypass flow paths depending on measured value of sensor.    USE - Used in fuel cell system (claimed) for producing hydrogen-rich heating gas from original fuel-containing hydrocarbon group compound.    ADVANTAGE - The fuel reformer has improved thermal efficiency and stability.    DETAILED DESCRIPTION - A fuel reformer has a reformation portion (142), a modifier (140), a raw material supplier, a sensor and a flow rate controller. The reformation portion accommodates a modification catalyst and a supply port to which a modification raw material containing several field fuels of raw material is supplied. The modifier modifies the modification raw material supplied from the supply port. The raw material supplier supplies the modification raw material to the supply port of the modifier. The sensor measures specific measured quantity in the modifier. The modifier has a heat exchanger (141a) which can be passed through before supplying the raw materials to the supply port of the modifier. The flow rate controller adjusts the flow rate allocation of the heat exchange flow path which passes through the heat exchanger and results in the supply port of the modifier. A bypass flow path (214) carries out bypass of the heat exchanger and results in the supply port of the modifier. The flow rate controller adjusts the flow rate allocation of the heat exchange flow path and the bypass flow path, depending on the measured value measured by the sensor. INDEPENDENT CLAIMS are included for the following:    (1) fuel cell system having a fuel cell (150) and a fuel reformer;    (2) moving component having a power supply containing a fuel cell, a fuel reformer, a motor for generating the driving force of the moving component and a driving circuit which actuates the motor using the electric power supplied from the power supply; and    (3) control of a modifier, which involves preparing the heat exchanger, the heat exchange flow path and the bypass flow path, measuring the specific measured quantity in the modifier, and adjusting the flow rate allocation of the heat exchange flow path and bypass flow path depending on the measured value.    DESCRIPTION OF DRAWING(S) - The figure shows the internal composition of the fuel cell system. (Drawing includes non-English language text).    Modifier (140)    Evaporation portion (141)    Heat exchanger (141a)    Reformation portion (142)    By-pass flow path (214)    Fuel cell (150)