A fuel cell system comprising: a fuel cell; a load value detecting means configured to detect a load value of a load of electric power or heat which is generated by equipment supplied with the electric power or the heat from said fuel cell system; a load value storage means configured to store a history of the load value detected by said load value detecting means; a load value predicting means configured to predict a load value which is going to be generated based on the history of the load value and to store the predicted load value as load value data; and a calculating means configured to calculate an amount of primary energy consumed to supply the electric power, an amount of carbon dioxide generated by supplying the electric power, or a cost necessary to supply the electric power, wherein scheduled start-up time of said fuel cell is decided based on the load value data, wherein the load value is a power value of a power load of the equipment supplied with the electric power from said fuel cell system, and the load value data is power value data, and wherein said calculating means calculates the amount of primary energy, the amount of carbon dioxide, or the cost, based on the power value data for a predetermined time period, for a case where said fuel cell supplies the electric power and for a case where a power system supplies the electric power, and values calculated by said calculating means are compared and start time of the time period is decided as the scheduled start-up time when the value calculated for the case where said power system supplies the electric power is larger than the value calculated for the case where said fuel cell supplies the electric power. a fuel cell; a load value detecting means configured to detect a load value of a load of electric power or heat which is generated by equipment supplied with the electric power or the heat from said fuel cell system; a load value storage means configured to store a history of the load value detected by said load value detecting means; a load value predicting means configured to predict a load value which is going to be generated based on the history of the load value and to store the predicted load value as load value data; and a calculating means configured to calculate an amount of primary energy consumed to supply the electric power, an amount of carbon dioxide generated by supplying the electric power, or a cost necessary to supply the electric power, wherein scheduled start-up time of said fuel cell is decided based on the load value data, wherein the load value is a power value of a power load of the equipment supplied with the electric power from said fuel cell system, and the load value data is power value data, and wherein said calculating means calculates the amount of primary energy, the amount of carbon dioxide, or the cost, based on the power value data for a predetermined time period, for a case where said fuel cell supplies the electric power and for a case where a power system supplies the electric power, and values calculated by said calculating means are compared and start time of the time period is decided as the scheduled start-up time when the value calculated for the case where said power system supplies the electric power is larger than the value calculated for the case where said fuel cell supplies the electric power.