A gas turbine, comprising: a compressor that compresses air; a combustor that burns compressed air compressed by the compressor with fuel to thereby generate combustion gas; and a turbine driven by the combustion gas generated by the combustor; the combustor including a transition piece that supplies the turbine with the combustion gas; the turbine including at least one turbine stage that includes one nozzle cascade and one blade cascade arranged in sequence from an upstream side along a turbine axial direction; nozzle end walls that define inner and outer peripheries of an annular combustion gas flow passage in the nozzle cascade in a first turbine stage, having anterior edges facing a posterior edge of the transition piece in the turbine axial direction; gaps between the anterior edges of the nozzle end walls and the posterior edge of the transition piece being sealed by seal members, the transition piece has flange portions that extend in a turbine radial direction, the flange portions being disposed on an inner peripheral wall and an outer peripheral wall of a combustion gas outlet portion at surfaces opposite to the combustion gas flow passage, characterised in that the nozzle end walls are thin plate-shaped members and have seal grooves in surfaces thereof facing the transition piece, the seal grooves extending in the turbine axial direction, the seal members each include a hook portion and a seal plate portion, the hook portion embracing the flange portion of the transition piece so as to slide in the turbine radial direction along the flange portion and the seal plate portion being inserted in the seal groove in the nozzle end wall, and the seal groove and the seal plate portion are configured to include a surface contact region in which a high temperature-side inner wall surface (21a-1) closer to the combustion gas flow passage of the seal groove and the seal plate portion are in surface contact with each other, a non-contact region disposed on a side closer to the transition piece than the surface contact region and having a gap interposed between the high temperature-side inner wall surface (21a-2) and a surface facing the seal plate portion, and a through hole provided at the seal plate portion so as to face the high temperature-side inner wall surface (21a-2) in the seal groove across the gap in the non-contact region. a compressor that compresses air; a combustor that burns compressed air compressed by the compressor with fuel to thereby generate combustion gas; and a turbine driven by the combustion gas generated by the combustor; the combustor including a transition piece that supplies the turbine with the combustion gas; the turbine including at least one turbine stage that includes one nozzle cascade and one blade cascade arranged in sequence from an upstream side along a turbine axial direction; nozzle end walls that define inner and outer peripheries of an annular combustion gas flow passage in the nozzle cascade in a first turbine stage, having anterior edges facing a posterior edge of the transition piece in the turbine axial direction; gaps between the anterior edges of the nozzle end walls and the posterior edge of the transition piece being sealed by seal members, the transition piece has flange portions that extend in a turbine radial direction, the flange portions being disposed on an inner peripheral wall and an outer peripheral wall of a combustion gas outlet portion at surfaces opposite to the combustion gas flow passage, characterised in that the nozzle end walls are thin plate-shaped members and have seal grooves in surfaces thereof facing the transition piece, the seal grooves extending in the turbine axial direction, the seal members each include a hook portion and a seal plate portion, the hook portion embracing the flange portion of the transition piece so as to slide in the turbine radial direction along the flange portion and the seal plate portion being inserted in the seal groove in the nozzle end wall, and the seal groove and the seal plate portion are configured to include a surface contact region in which a high temperature-side inner wall surface (21a-1) closer to the combustion gas flow passage of the seal groove and the seal plate portion are in surface contact with each other, a non-contact region disposed on a side closer to the transition piece than the surface contact region and having a gap interposed between the high temperature-side inner wall surface (21a-2) and a surface facing the seal plate portion, and a through hole provided at the seal plate portion so as to face the high temperature-side inner wall surface (21a-2) in the seal groove across the gap in the non-contact region. a surface contact region in which a high temperature-side inner wall surface (21a-1) closer to the combustion gas flow passage of the seal groove and the seal plate portion are in surface contact with each other, a non-contact region disposed on a side closer to the transition piece than the surface contact region and having a gap interposed between the high temperature-side inner wall surface (21a-2) and a surface facing the seal plate portion, and a through hole provided at the seal plate portion so as to face the high temperature-side inner wall surface (21a-2) in the seal groove across the gap in the non-contact region.