A gas turbine plant comprising: a gas turbine configured to receive fuel in accordance with a required output, combust the fuel, and be driven by a combustion gas generated by combusting the fuel; an exhaust line configured to guide an exhaust gas exhausted from the gas turbine to an outside; a carbon dioxide recovery device provided on the exhaust line and configured to recover carbon dioxide contained in the exhaust gas flowing through the exhaust line; a circulation line branching from a position on the exhaust line on an upstream side in a flow direction of the exhaust gas with the carbon dioxide recovery device as a reference and connected to the gas turbine; a bypass line branching from a position on the exhaust line on a downstream side of the circulation line in the flow direction and the upstream side of the carbon dioxide recovery device, bypassing the carbon dioxide recovery device, and connected to a position on the exhaust line on a downstream side of the carbon dioxide recovery device; a densitometer provided on the exhaust line and configured to detect a carbon dioxide concentration in the exhaust gas; and a control device, characterized in that the gas turbine plant further comprises: a first valve device provided on the circulation line; a second valve device provided on the bypass line; and a third valve device provided on the exhaust line at a position between the bypass line and the carbon dioxide recovery device, and the control device is configured to adjust opening degrees of the first valve device, the second valve device, and the third valve device based on at least one of an operation state of the gas turbine and the carbon dioxide concentration. a gas turbine configured to receive fuel in accordance with a required output, combust the fuel, and be driven by a combustion gas generated by combusting the fuel; an exhaust line configured to guide an exhaust gas exhausted from the gas turbine to an outside; a carbon dioxide recovery device provided on the exhaust line and configured to recover carbon dioxide contained in the exhaust gas flowing through the exhaust line; a circulation line branching from a position on the exhaust line on an upstream side in a flow direction of the exhaust gas with the carbon dioxide recovery device as a reference and connected to the gas turbine; a bypass line branching from a position on the exhaust line on a downstream side of the circulation line in the flow direction and the upstream side of the carbon dioxide recovery device, bypassing the carbon dioxide recovery device, and connected to a position on the exhaust line on a downstream side of the carbon dioxide recovery device; a densitometer provided on the exhaust line and configured to detect a carbon dioxide concentration in the exhaust gas; and a control device, characterized in that the gas turbine plant further comprises: a first valve device provided on the circulation line; a second valve device provided on the bypass line; and a third valve device provided on the exhaust line at a position between the bypass line and the carbon dioxide recovery device, and a first valve device provided on the circulation line; a second valve device provided on the bypass line; and a third valve device provided on the exhaust line at a position between the bypass line and the carbon dioxide recovery device, and the control device is configured to adjust opening degrees of the first valve device, the second valve device, and the third valve device based on at least one of an operation state of the gas turbine and the carbon dioxide concentration.