To provide a gas turbine and a transition piece capable of lowering costs and improving performance of the gas turbine by decreasing the tip clearance.

In the gas turbine equipped with a compressor 1 for generating compressed air, a combustor 3 for burning fuel with compressed air from the compressor 1 and generating combustion gas, and a turbine 4 rotationally driven by the combustion gas from the combustor 3, a heat exchanger 22 arranged on a transition piece 15 introducing the combustion gas from the combustor 3 to the turbine 4 and heating a part of the compressed air extracted from the compressor 1 by the combustion gas and a casing passage 23 which is formed on a casing 16 of the turbine 4 and through which the air heated by the heat exchanger 22 flows in are provided.