A fuel treatment apparatus for a fuel cell, comprising: a reforming reactor configured for producing reformed gas from a gas mixture of water and a raw material for power generation; a burner configured for supplying heat to the reforming reactor; a water gas reactor including a reactor main body configured for being supplied with the reformed gas from the reforming reactor and reducing concentration of carbon monoxide in the reformed gas and a cooling flow path that is installed in the reactor main body; and a valve configured for controlling a supply of a cooling medium to the cooling flow path according to a startup or a normal operation of the water gas reactor; wherein the burner is configured for being supplied with burner fuel and burner air through a fuel pipe and an air pipe, and the cooling medium is the burner air supplied to the burner; wherein the cooling flow path is connected to a supply pipe and a discharge pipe outside the reactor main body, the supply pipe is connected to the air pipe, and the discharge pipe is connected to any one of the air pipe and the fuel pipe; wherein the reactor main body has a catalyst therein, the catalyst positioned in the reactor main body at a predetermined distance from upper and lower ends of the reactor main body, and an inlet pipe and an outlet pipe for the reformed gas are connected to an upper portion of a sidewall and a lower portion of the sidewall of the reactor main body that abut against the catalyst, the sidewall of the reactor main body connecting the upper and lower ends of the reactor main body; wherein the cooling flow path includes a first cover plate which covers an upper end of the catalyst, a second cover plate which covers a lower end of the catalyst, and a plurality of cooling pipes which is connected to the first cover plate and the second cover plate and penetrates the catalyst, and the supply pipe and the discharge pipe for the cooling medium are connected to lower and upper ends of the reactor main body. a reforming reactor configured for producing reformed gas from a gas mixture of water and a raw material for power generation; a burner configured for supplying heat to the reforming reactor; a water gas reactor including a reactor main body configured for being supplied with the reformed gas from the reforming reactor and reducing concentration of carbon monoxide in the reformed gas and a cooling flow path that is installed in the reactor main body; and a valve configured for controlling a supply of a cooling medium to the cooling flow path according to a startup or a normal operation of the water gas reactor; wherein the burner is configured for being supplied with burner fuel and burner air through a fuel pipe and an air pipe, and the cooling medium is the burner air supplied to the burner; wherein the cooling flow path is connected to a supply pipe and a discharge pipe outside the reactor main body, the supply pipe is connected to the air pipe, and the discharge pipe is connected to any one of the air pipe and the fuel pipe; wherein the reactor main body has a catalyst therein, the catalyst positioned in the reactor main body at a predetermined distance from upper and lower ends of the reactor main body, and an inlet pipe and an outlet pipe for the reformed gas are connected to an upper portion of a sidewall and a lower portion of the sidewall of the reactor main body that abut against the catalyst, the sidewall of the reactor main body connecting the upper and lower ends of the reactor main body; wherein the cooling flow path includes a first cover plate which covers an upper end of the catalyst, a second cover plate which covers a lower end of the catalyst, and a plurality of cooling pipes which is connected to the first cover plate and the second cover plate and penetrates the catalyst, and the supply pipe and the discharge pipe for the cooling medium are connected to lower and upper ends of the reactor main body.