1. 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 an operation control means configured to decide scheduled start-up time of said fuel cell based on the load value data predicted by said load value predicting means.