NOVELTY - Fuel cell system comprises a hydrogen adsorbing alloy tank, a heat exchange unit, a first passage to allow hydrogen gas from the hydrogen tank to flow into the fuel cell, a second passage connecting the first passage and the hydrogen adsorbing alloy tank, and control unit which heats the fuel cell when its temperature is equal to or lower than reference temperature.    USE - The fuel cell system is to be mounted on a vehicle (claimed), e.g. an automobile.    ADVANTAGE - The inventive fuel cell is capable of controlling the temperature of a fuel cell. The fuel cell is heated with the heat generated when the hydrogen gas is adsorbed in the hydrogen adsorbing alloy tank, thus eliminating the need for an electric heater and a combustion heater as used conventionally and eliminating the need for a large-capacity battery.    DETAILED DESCRIPTION - Fuel cell system comprises a hydrogen tank and a fuel cell connected and adapted to receive hydrogen gas and generate electric power; a hydrogen adsorbing alloy tank (300) connected to receive the hydrogen gas from the hydrogen tank and adapted to adsorb the received hydrogen gas in the hydrogen adsorbing alloy and to discharge the hydrogen gas from the hydrogen adsorbing alloy to the fuel cell; a heat exchange unit (58, 60) connected and adapted to circulate a heat exchange medium to the fuel cell and the hydrogen adsorbing alloy tank to cause heat exchange at least between the fuel cell and the hydrogen adsorbing alloy tank; a first passage (50) connecting the hydrogen tank and the fuel cell to allow hydrogen gas from the hydrogen tank to flow into the fuel cell; a second passage (54) branching from the first passage and connecting the first passage and the hydrogen adsorbing alloy tank; and a control unit which heats the fuel cell when its temperature is equal to or lower than a first reference temperature by supplying the hydrogen gas from the hydrogen tank to the hydrogen adsorbing alloy tank through the first passage and the second passage so that the hydrogen gas is adsorbed in the hydrogen adsorbing alloy tank with generation of heat, and transmitting the generated heat to the fuel cell by the heat exchange medium in the heat exchange unit. INDEPENDENT CLAIMS are also included for:    (a) a vehicle comprising a fuel cell system; and    (b) a method of controlling a fuel cell system, which involves heating the fuel cell when a temperature of the fuel cell is equal to or lower than a first reference temperature by supplying the hydrogen gas from the hydrogen tank to the hydrogen adsorbing alloy tank so that the hydrogen gas is adsorbed in the hydrogen adsorbing alloy tank with generation of heat, and transmitting the generated heat to the fuel cell by a heat exchange medium.    DESCRIPTION OF DRAWING(S) - The figure shows the structure of a fuel cell system.    First passage (50)    Second passage (54)    Heat exchange unit (58, 60)    Hydrogen adsorbing alloy tank (300)