Combustor and gas turbine

A combustor comprising:

• a transition piece having a cylindrical shape, and including an inlet of combustion gas at one end and an outlet of the combustion gas at another end, and configured to lead the combustion gas entering from the inlet to flow out from the outlet so as to introduce the combustion gas into a turbine;
• a cooling medium introduction unit provided at least on a portion of an outer periphery portion in a peripheral direction at an outlet side of the transition piece and in which a cooling medium is introduced;
• a cooling medium inlet provided on the cooling medium introduction unit and configured to introduce the cooling medium into the cooling medium introduction unit;
• a cooling portion provided on a portion ranging from the outlet of the transition piece to a predetermined position toward the inlet, connected to the cooling medium introduction unit so as to pass the cooling medium from the cooling medium introduction unit toward the inlet from the outlet;
• and
• a branching portion provided at least in a predetermined area in the peripheral direction of the transition piece including a portion farthest from the cooling medium inlet and configured to allow some of the cooling medium inside the cooling medium introduction unit to flow into the cooling portion at a portion closer to the inlet than the connecting portion where the cooling portion is connected to the cooling medium introduction unit, wherein
• the branching portion is provided at least at a central axis of rotation side of the turbine of the transition piece.