A fossil fuel combustion thermal power system including a carbon dioxide separation and capture unit comprising: a fossil fuel combustion thermal power system including a boiler for burning fossil fuel and generating steam and a steam turbine driven by the steam generated by the boiler for generating power, and a carbon dioxide separation and capture unit including an absorption tower for absorbing and capturing carbon dioxide included in the exhaust gas discharged from the boiler by burning fossil fuel in the boiler of the fossil fuel combustion thermal power system and a reproduction tower of an absorbing solution for separating carbon dioxide from the absorbing solution absorbing carbon dioxide by circulating the absorbing solution between the reproduction tower and the absorption tower, wherein the fossil fuel combustion thermal power system including the carbon dioxide separation and capture unit further comprises: a back-pressure turbine driven by extraction steam extracted from the turbine of the fossil fuel combustion thermal power system through an extraction pipe; a reboiler for supplying heating steam to the reproduction tower of the carbon dioxide separation and capture unit; a steam pipe for supplying steam flowing down through the back-pressure turbine of the fossil fuel combustion thermal power system to the reboiler as a heat source; characterized in that the fossil fuel combustion thermal power system including the carbon dioxide separation and capture unit further comprises: an emergency relief pipe (112, 156, 164) interconnected to the extraction pipe for supplying the extraction steam extracted from the turbine side of the fossil fuel combustion thermal power system to the back-pressure turbine for permitting the extraction steam flowing down through the extraction pipe (105, 150) to bypass the back-pressure turbine and flow down to a condenser through the emergency relief pipe (112, 156, 164) when an operation of the carbon dioxide separation and capture unit stops urgently; and an emergency relief valve (111, 156, 163) installed on the emergency relief pipe (112, 156, 164) for controlling flow of the extraction steam through the emergency relief pipe. a fossil fuel combustion thermal power system including a boiler for burning fossil fuel and generating steam and a steam turbine driven by the steam generated by the boiler for generating power, and a carbon dioxide separation and capture unit including an absorption tower for absorbing and capturing carbon dioxide included in the exhaust gas discharged from the boiler by burning fossil fuel in the boiler of the fossil fuel combustion thermal power system and a reproduction tower of an absorbing solution for separating carbon dioxide from the absorbing solution absorbing carbon dioxide by circulating the absorbing solution between the reproduction tower and the absorption tower, wherein the fossil fuel combustion thermal power system including the carbon dioxide separation and capture unit further comprises: a back-pressure turbine driven by extraction steam extracted from the turbine of the fossil fuel combustion thermal power system through an extraction pipe; a reboiler for supplying heating steam to the reproduction tower of the carbon dioxide separation and capture unit; a steam pipe for supplying steam flowing down through the back-pressure turbine of the fossil fuel combustion thermal power system to the reboiler as a heat source; characterized in that the fossil fuel combustion thermal power system including the carbon dioxide separation and capture unit further comprises: an emergency relief pipe (112, 156, 164) interconnected to the extraction pipe for supplying the extraction steam extracted from the turbine side of the fossil fuel combustion thermal power system to the back-pressure turbine for permitting the extraction steam flowing down through the extraction pipe (105, 150) to bypass the back-pressure turbine and flow down to a condenser through the emergency relief pipe (112, 156, 164) when an operation of the carbon dioxide separation and capture unit stops urgently; and an emergency relief valve (111, 156, 163) installed on the emergency relief pipe (112, 156, 164) for controlling flow of the extraction steam through the emergency relief pipe. a back-pressure turbine driven by extraction steam extracted from the turbine of the fossil fuel combustion thermal power system through an extraction pipe; a reboiler for supplying heating steam to the reproduction tower of the carbon dioxide separation and capture unit; a steam pipe for supplying steam flowing down through the back-pressure turbine of the fossil fuel combustion thermal power system to the reboiler as a heat source; characterized in that the fossil fuel combustion thermal power system including the carbon dioxide separation and capture unit further comprises: an emergency relief pipe (112, 156, 164) interconnected to the extraction pipe for supplying the extraction steam extracted from the turbine side of the fossil fuel combustion thermal power system to the back-pressure turbine for permitting the extraction steam flowing down through the extraction pipe (105, 150) to bypass the back-pressure turbine and flow down to a condenser through the emergency relief pipe (112, 156, 164) when an operation of the carbon dioxide separation and capture unit stops urgently; and an emergency relief valve (111, 156, 163) installed on the emergency relief pipe (112, 156, 164) for controlling flow of the extraction steam through the emergency relief pipe.