A fuel cell system comprising: n fuel cell modules operated for power generation by electrochemical reactions of a fuel gas and an oxygen-containing gas, where n is a natural number of 2 or more; and a control device for controlling a power generation amount of each of the fuel cell modules; wherein an m-th fuel cell module, where m is a natural number smaller than n, comprises: an m-th exhaust gas discharge channel for discharging an exhaust gas from the m-th fuel cell module; and an m-th exhaust gas supply channel branched from the m-th exhaust gas discharge channel, for supplying the exhaust gas from the m-th fuel cell module to an (m+1)-th fuel cell module (12(m+1)) for warming up the (m+1)-th fuel cell module (12(m+1)), and wherein the control device comprises: a fuel utilization ratio controller for controlling the fuel utilization ratio of the m-th fuel cell module based on the power generation amount of the m-th fuel cell module and the temperature of the (m+1)-th fuel cell module (12(m+1)); an exhaust gas flow rate controller for controlling the flow rate of the exhaust gas supplied from the m-th exhaust gas discharge channel to the (m+1)-th fuel cell module (12(m+1)) through the m-th exhaust gas supply channel; a power generation amount controller for controlling the power generation amounts of the m-th fuel cell module and the (m+1)-th fuel cell module (12(m+1)); and a comparator for comparing the power generation amount of the m-th fuel cell module with a predetermined first power generation amount set value, for comparing the power generation amount of the m-th fuel cell module with a predetermined second power generation amount set value which is larger than the first power generation amount set value, and for comparing the temperature of the (m+1)-the fuel cell module (12(m+1)) with a predetermined temperature set value, wherein when the current power generation amount of the m-th fuel cell module is equal to or more than the first power generation amount set value, and the temperature of the (m+1)-th fuel cell module (12(m+1)) is less than the temperature set value, the fuel utilization ratio controller implements control to decrease the fuel utilization ratio of the m-th fuel cell module, and the exhaust gas flow rate controller implements control to increase the flow rate of the exhaust gas supplied to the (m+1)-th fuel cell module (12(m+1)), and when the current power generation amount of the m-th fuel cell module is equal to or more than the second power generation amount set value, the supply of the exhaust gas to the m-th exhaust gas supply channel is stopped. n fuel cell modules operated for power generation by electrochemical reactions of a fuel gas and an oxygen-containing gas, where n is a natural number of 2 or more; and a control device for controlling a power generation amount of each of the fuel cell modules; an m-th exhaust gas discharge channel for discharging an exhaust gas from the m-th fuel cell module; and an m-th exhaust gas supply channel branched from the m-th exhaust gas discharge channel, for supplying the exhaust gas from the m-th fuel cell module to an (m+1)-th fuel cell module (12(m+1)) for warming up the (m+1)-th fuel cell module (12(m+1)), a fuel utilization ratio controller for controlling the fuel utilization ratio of the m-th fuel cell module based on the power generation amount of the m-th fuel cell module and the temperature of the (m+1)-th fuel cell module (12(m+1)); an exhaust gas flow rate controller for controlling the flow rate of the exhaust gas supplied from the m-th exhaust gas discharge channel to the (m+1)-th fuel cell module (12(m+1)) through the m-th exhaust gas supply channel; a power generation amount controller for controlling the power generation amounts of the m-th fuel cell module and the (m+1)-th fuel cell module (12(m+1)); and a comparator for comparing the power generation amount of the m-th fuel cell module with a predetermined first power generation amount set value, for comparing the power generation amount of the m-th fuel cell module with a predetermined second power generation amount set value which is larger than the first power generation amount set value, and for comparing the temperature of the (m+1)-the fuel cell module (12(m+1)) with a predetermined temperature set value,