NOVELTY - A fuel cell system comprises a fuel tank for storing a fuel; an evaporator for generating a fuel gas; a reforming reactor for generating reforming gas containing hydrogen from the fuel gas; a combustor; a fuel cell portion for generating electricity; a boiling point temperature estimator; a vapor temperature measuring portion; and a flow rate control portion.    USE - Used in a moving body e.g. an automobile.    ADVANTAGE - The fuel cell system has high efficiency and stability due to stable supply of the fuel gas from the evaporator to the reforming reactor.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel tank for storing a fuel; an evaporator for evaporating the fuel to generate fuel gas; a reforming reactor for generating reforming gas containing hydrogen from the fuel gas; a combustor for burning the fuel or the reforming gas to supply heat to the evaporator; a fuel cell portion for generating electricity using the hydrogen contained in the reforming gas; a boiling point temperature estimator for estimating a boiling point temperature of the fuel in the evaporator based on an operation pressure of the evaporator; a vapor temperature measuring portion for measuring a vapor temperature of the fuel gas in the evaporator; and a flow rate control portion for increasing a flow rate of the fuel or the reforming gas burnt in the combustor when a value obtained by subtracting the boiling point temperature from the vapor temperature becomes below a predetermined value.    An INDEPENDENT CLAIM is also included for the control of the fuel cell system by:    (a) estimating the boiling point temperature of the fuel in the evaporator based on an operation pressure of the evaporator using the boiling point temperature estimator;    (b) measuring a vapor temperature of the fuel gas in the evaporator using the vapor temperature measuring portion; and    (c) increasing the flow rate of the fuel or the reforming gas burnt in the combustor when a value obtained by subtracting the boiling point temperature from the vapor temperature becomes below a predetermined value.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a fuel cell system.