Transition piece of combustor, gas turbine having the same, and producing method for transition piece

A transition piece of a combustor which has a trunk part formed in a cylindrical shape, which allows high temperature combustion gas to flow on an inner periphery side of this trunk part, and which supplies the combustion gas to a turbine, the transition piece comprising:

• a cylindrical trunk main body;
• a cylindrical exit trunk part which is connected to a downstream end of said trunk main body, and which cooperates with the trunk main body to constitute said trunk part;
• and
• a flange which extends from a downstream end part of said exit trunk part toward an outer periphery side of the exit trunk part,
• wherein
• said exit trunk part and said flange are of a single-piece product,
• and on said exit trunk part, at a position on an upstream side of said flange and along the flange, there is formed a groove which recesses from an outer periphery side toward an inner periphery side and which extends around the circumferential direction, and there is formed a cooling fluid passage extending in a direction along the axis of said trunk part and which opens at the groove.