A power generation system comprising: a combustor configured to combust a fuel; a power generation unit configured to utilize energy obtained from the combustor when generating electric power; a fuel supply unit configured to supply the fuel to the combustor; an air supply unit configured to supply combustion air to the combustor; a discharged gas passage through which a discharged gas from the combustor flows; a CO detector configured to detect CO in the discharged gas; and characterized by a temperature detector configured to detect a temperature of the discharged gas; and a controller configured to, when the discharged gas is flowing through the discharged gas passage, perform at least one of an operation of detecting an abnormality of the discharged gas passage based on a difference between detected temperatures of the temperature detector by changing heated amounts of the discharged gas heated by a heater (8A, 8B, 8C, 11) and an operation of detecting the abnormality of the discharged gas passage based on a difference between two detected temperatures of the temperature detector, wherein the controller is configured to change the flow rate of the discharged gas by changing outputs of at least one of the fuel supply unit and the air supply unit and to detect the temperature of the temperature detector prior to and after said changing of outputs, such that the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage exists and the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage does not exist become different from each other. a combustor configured to combust a fuel; a power generation unit configured to utilize energy obtained from the combustor when generating electric power; a fuel supply unit configured to supply the fuel to the combustor; an air supply unit configured to supply combustion air to the combustor; a discharged gas passage through which a discharged gas from the combustor flows; a CO detector configured to detect CO in the discharged gas; and characterized by a temperature detector configured to detect a temperature of the discharged gas; and a controller configured to, when the discharged gas is flowing through the discharged gas passage, perform at least one of an operation of detecting an abnormality of the discharged gas passage based on a difference between detected temperatures of the temperature detector by changing heated amounts of the discharged gas heated by a heater (8A, 8B, 8C, 11) and an operation of detecting the abnormality of the discharged gas passage based on a difference between two detected temperatures of the temperature detector, wherein the controller is configured to change the flow rate of the discharged gas by changing outputs of at least one of the fuel supply unit and the air supply unit and to detect the temperature of the temperature detector prior to and after said changing of outputs, such that the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage exists and the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage does not exist become different from each other. an operation of detecting an abnormality of the discharged gas passage based on a difference between detected temperatures of the temperature detector by changing heated amounts of the discharged gas heated by a heater (8A, 8B, 8C, 11) and an operation of detecting the abnormality of the discharged gas passage based on a difference between two detected temperatures of the temperature detector, wherein the controller is configured to change the flow rate of the discharged gas by changing outputs of at least one of the fuel supply unit and the air supply unit and to detect the temperature of the temperature detector prior to and after said changing of outputs, such that the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage exists and the difference between the two detected temperatures of the temperature detector in a case where the abnormality of the discharged gas passage does not exist become different from each other.