A gas turbine apparatus comprising: a first driving shaft and a second driving shaft, wherein the first driving shaft is provided as an inner shaft and the second driving shaft is provided as an outer shaft disposed to surround the inner shaft and having a hollow shape and is concentric with the first driving shaft; a compressor configured to receive power from the first driving shaft and the second driving shaft, suck air, and compress the sucked air at high pressure, wherein the compressor includes one or more first compressor blades and one or more second compressor blades wherein the first compressor blades and the second compressor blades are alternately arranged along an axial direction of the compressor; a combustor configured to mix the compressed air with fuel, and combust the fuel mixture to generate combustion gas; and a turbine connected to the first driving shaft and the second driving shaft and configured to rotate while the combustion gas passes through the turbine, the turbine comprising one or more first turbine blades connected to the first driving shaft and configured to rotate in a first direction and one or more second turbine blades connected to the second driving shaft and configured to rotate in a second direction opposite to the first direction, the one or more first turbine blades and the one or more second turbine blades being alternately arranged along an axial direction of the turbine, and wherein the first compressor blades are connected to the first driving shaft and configured to rotate in the first direction and the second compressor blades are connected to the second driving shaft and configured to rotate in the second direction, characterized in that: the width of the blade part of each turbine blade, corresponding to a flow area with which the combustion gas is contacted while flowing, is gradually increased toward the downstream side along the flow direction of the combustion gas, and a distance between a radially outer limit of the flow area and a central-axis line of the first driving shaft is constantly maintained along a direction of the central-axis line. a first driving shaft and a second driving shaft, wherein the first driving shaft is provided as an inner shaft and the second driving shaft is provided as an outer shaft disposed to surround the inner shaft and having a hollow shape and is concentric with the first driving shaft; a compressor configured to receive power from the first driving shaft and the second driving shaft, suck air, and compress the sucked air at high pressure, wherein the compressor includes one or more first compressor blades and one or more second compressor blades wherein the first compressor blades and the second compressor blades are alternately arranged along an axial direction of the compressor; a combustor configured to mix the compressed air with fuel, and combust the fuel mixture to generate combustion gas; and a turbine connected to the first driving shaft and the second driving shaft and configured to rotate while the combustion gas passes through the turbine, the turbine comprising one or more first turbine blades connected to the first driving shaft and configured to rotate in a first direction and one or more second turbine blades connected to the second driving shaft and configured to rotate in a second direction opposite to the first direction, the one or more first turbine blades and the one or more second turbine blades being alternately arranged along an axial direction of the turbine, and wherein the first compressor blades are connected to the first driving shaft and configured to rotate in the first direction and the second compressor blades are connected to the second driving shaft and configured to rotate in the second direction, characterized in that: the width of the blade part of each turbine blade, corresponding to a flow area with which the combustion gas is contacted while flowing, is gradually increased toward the downstream side along the flow direction of the combustion gas, and a distance between a radially outer limit of the flow area and a central-axis line of the first driving shaft is constantly maintained along a direction of the central-axis line.