A fuel cell system connected with a load, comprising: a fuel cell; a secondary battery electrically connected with the fuel cell; means for obtaining data concerning electric energy stored in the secondary battery; first determination means for determining one from a plurality of start-up modes differing from each other in energy consumption, for the fuel cell system based on the obtained data concerning electric energy stored in the secondary battery; and memory means storing at least one threshold value for determining the start-up mode of the fuel cell system, wherein the first determination means determines the start-up mode of the fuel cell system based on the data concerning electric energy stored in the secondary battery and the at least one threshold value stored in the memory means; wherein the at least one threshold value includes a first threshold value representing energy necessary for starting the fuel cell system, the first determination means including means for determining on whether or not the fuel cell system is started, based on the data concerning electric energy stored in the secondary battery and the first threshold value; wherein the at least one threshold value includes a second threshold value representing normal-consumption energy necessary for starting the fuel cell system in a normal mode, the first determination means including means for determining on whether the fuel cell system is started in the normal mode or in a low consumption mode, based on the data concerning electric energy stored in the secondary battery and the second threshold value; wherein in the low consumption mode restrictions are placed on operations of system components when the fuel cell system is started; wherein the fuel cell is operated at a lower output voltage when the fuel cell system is started in a low consumption mode than when started in a normal mode at a same temperature of the fuel cell; and wherein, when the fuel cell system is started in the low consumption mode, a predetermined voltage for determining on whether or not the fuel cell is disconnected from the secondary battery is set to a lower value than when started in the normal mode, wherein determining on whether or not the fuel cell is disconnected from the secondary battery is based on the fuel cell's output voltage and the predetermined voltage. a fuel cell; a secondary battery electrically connected with the fuel cell; means for obtaining data concerning electric energy stored in the secondary battery; first determination means for determining one from a plurality of start-up modes differing from each other in energy consumption, for the fuel cell system based on the obtained data concerning electric energy stored in the secondary battery; and memory means storing at least one threshold value for determining the start-up mode of the fuel cell system, wherein the first determination means determines the start-up mode of the fuel cell system based on the data concerning electric energy stored in the secondary battery and the at least one threshold value stored in the memory means; wherein the at least one threshold value includes a first threshold value representing energy necessary for starting the fuel cell system, the first determination means including means for determining on whether or not the fuel cell system is started, based on the data concerning electric energy stored in the secondary battery and the first threshold value; wherein the at least one threshold value includes a second threshold value representing normal-consumption energy necessary for starting the fuel cell system in a normal mode, the first determination means including means for determining on whether the fuel cell system is started in the normal mode or in a low consumption mode, based on the data concerning electric energy stored in the secondary battery and the second threshold value; wherein in the low consumption mode restrictions are placed on operations of system components when the fuel cell system is started; wherein the fuel cell is operated at a lower output voltage when the fuel cell system is started in a low consumption mode than when started in a normal mode at a same temperature of the fuel cell; and wherein, when the fuel cell system is started in the low consumption mode, a predetermined voltage for determining on whether or not the fuel cell is disconnected from the secondary battery is set to a lower value than when started in the normal mode, wherein determining on whether or not the fuel cell is disconnected from the secondary battery is based on the fuel cell's output voltage and the predetermined voltage.