Turbine blade, manufacturing method for turbine blade, and gas turbine

A manufacturing method for a turbine blade including a plurality of cooling passages along a blade height direction that are disposed at intervals in a front and rear direction of a blade, the manufacturing method comprising:

• forming a first cooling passage by electrolytic machining while adjusting at least one of a current value and a machining speed from a front end toward a base end of the turbine blade, the first cooling passage having
• a first cooling hole that has a first end opening toward the front end, and that has an inner diameter that is constant along the blade height direction, and
• a second cooling hole that has a first end communicating with a second end of the first cooling hole without a level difference, and that has an inner diameter that is increased by a first expansion ratio toward the base end;
• and
• forming a second cooling passage by electrolytic machining while adjusting at least one of a current value and a machining speed from the front end toward the base end of the turbine blade, the second cooling passage having an inner diameter that is increased by a second expansion ratio along the blade height direction, the second expansion ratio being smaller than the first expansion ratio, wherein
• a length from the first end of the first cooling hole on the front end of the turbine blade to a position where the first cooling hole and the second cooling hole are communicated with is 40% to 60% of a length from the first end of the first cooling hole to a gas path surface on the base end of the turbine blade.