NOVELTY - A fuel cell has reformer for reforming hydrocarbon type fuel and manufactures hydrogen-containing-gas and has modification-catalyst layer, and high-temperature-form fuel cell which generates electric power. The temperature of reforming catalyst layer is increased while measuring the temperature of reforming catalysis layer. The fuel flow rate of the electrode is more than the current value of the fuel flow rate, and then fuel of predetermined flow rate is supplied to the catalyst layer. Thus, the fuel cell system is started.    USE - Starting of fuel cell system for electric power generation used in co-generation system.    ADVANTAGE - The method is reliable and efficiently prevents oxidation/degradation of anode by performing reformation.    DETAILED DESCRIPTION - A fuel cell has reformer for reforming hydrocarbon type fuel and manufactures hydrogen-containing-gas and has modification-catalyst layer, and high-temperature-form fuel cell which generates electric power using hydrogen-containing-gas. The start method of fuel cell system satisfies the following characteristics. Two or more flow rates (M) of fuel cell are preset as fuel flow rate upon start completion (Fm) and satisfies relation: F1,Fj is more than 0 and less than Fj+1 (A), where j is 1 to M-1. The temperature of reforming catalyst layer is increased while measuring the temperature of reforming catalysis layer (B). A fuel flow rate (Fr) capable of reformation is calculated with respect to measured temperature (C). If Fr is less than F1 and fuel flow rate is Fj then fuel flow rate is 0. The fuel flow rate of reformation (Fr) is less than Fj and more than Fj+1. The fuel electrode is Fm if Fm is Fr or more (D). The fuel flow rate of the electrode is more than the current value of the fuel flow rate, then fuel of predetermined flow rate is supplied to the catalyst layer and reformed gas obtained by reformation is supplied to the fuel cell anode (E). The steps (C-E) are repeated such that the fuel supply amount to the catalyst layer reaches the fuel flow rate upon start completion. Thus, the fuel cell system is started. An INDEPENDENT CLAIM is included for fuel cell system.