An engine exhaust gas energy recovery device comprising: an exhaust gas turbocharger comprising a turbine and a compressor, the turbine arranged to be driven by the exhaust gas discharged from an engine comprising an engine body, the compressor being arranged to compression-transport outside air to the engine body by driving the turbine; a first exhaust pipe connecting the exhaust gas turbocharger to an exhaust manifold of the engine; a power turbine arranged to be driven by the exhaust gas; a second exhaust pipe connecting the exhaust manifold to the power turbine; an exhaust gas flow-rate control valve being provided part way along the second exhaust pipe so as to control the flow-rate of the exhaust gas fed to the power turbine; a bypass pipe being connected to the second exhaust pipe which is provided on the upstream side of the exhaust gas flow-rate control valve so as to bypass the power turbine; an exhaust gas bypass control valve which is provided part way along the bypass pipe and which is arranged to control the flow-rate of the exhaust gas bypassing the power turbine; an orifice provided part way along the bypass pipe and on the downstream side of the exhaust gas bypass control valve, the orifice being arranged so that an exhaust gas flow-rate through the orifice in a case where the exhaust gas flow-rate control valve is fully closed is the same as an exhaust gas flow-rate through the exhaust gas flow-rate control valve in a case where the engine body is under a high load condition and the exhaust gas bypass control valve is fully closed and the exhaust gas flow-rate control valve is fully opened; an engine load detecting sensor arranged to detect the load of the engine; an engine speed detecting sensor arranged to detect the speed (Ne) of the engine; a cylinder pressure detecting sensor arranged to detect a cylinder pressure (Pcyl) of the engine; and a control device arranged to compute, using a database, the optimal compression pressure (PcompO) and the optimal cylinder maximum pressure (PmaxO) at which a fuel consumption rate of the engine becomes the optimum operating state on the basis of each value detected by the engine load detecting sensor and the engine speed detecting sensor, wherein the control device is arranged to control an exhaust valve closing timing so that a compression pressure agrees with the computed optimal compression pressure (PcompO), and to control a fuel injection timing so that a cylinder maximum pressure agrees with the computed optimal cylinder maximum pressure (PmaxO), an exhaust gas turbocharger comprising a turbine and a compressor, the turbine arranged to be driven by the exhaust gas discharged from an engine comprising an engine body, the compressor being arranged to compression-transport outside air to the engine body by driving the turbine; a first exhaust pipe connecting the exhaust gas turbocharger to an exhaust manifold of the engine; a power turbine arranged to be driven by the exhaust gas; a second exhaust pipe connecting the exhaust manifold to the power turbine; an exhaust gas flow-rate control valve being provided part way along the second exhaust pipe so as to control the flow-rate of the exhaust gas fed to the power turbine; a bypass pipe being connected to the second exhaust pipe which is provided on the upstream side of the exhaust gas flow-rate control valve so as to bypass the power turbine; an exhaust gas bypass control valve which is provided part way along the bypass pipe and which is arranged to control the flow-rate of the exhaust gas bypassing the power turbine; an orifice provided part way along the bypass pipe and on the downstream side of the exhaust gas bypass control valve, the orifice being arranged so that an exhaust gas flow-rate through the orifice in a case where the exhaust gas flow-rate control valve is fully closed is the same as an exhaust gas flow-rate through the exhaust gas flow-rate control valve in a case where the engine body is under a high load condition and the exhaust gas bypass control valve is fully closed and the exhaust gas flow-rate control valve is fully opened; an engine load detecting sensor arranged to detect the load of the engine; an engine speed detecting sensor arranged to detect the speed (Ne) of the engine; a cylinder pressure detecting sensor arranged to detect a cylinder pressure (Pcyl) of the engine; and a control device arranged to compute, using a database, the optimal compression pressure (PcompO) and the optimal cylinder maximum pressure (PmaxO) at which a fuel consumption rate of the engine becomes the optimum operating state on the basis of each value detected by the engine load detecting sensor and the engine speed detecting sensor, wherein the control device is arranged to control an exhaust valve closing timing so that a compression pressure agrees with the computed optimal compression pressure (PcompO), and to control a fuel injection timing so that a cylinder maximum pressure agrees with the computed optimal cylinder maximum pressure (PmaxO),