A gas turbine combustor provided with: a plurality of swirler tubes that are disposed inside a combustor basket and impart a swirl to a premixed gas, the premixed gas being obtained by premixing a fuel and air for combustion; and an outer ring that is disposed between the plurality of swirler tubes and the combustor basket with a gap provided between the outer ring and the combustor basket, and generates film-shaped air inside a combustor transition piece connected to the combustor basket via injection through the gap into the combustor transition piece, and at a downstream end of the outer ring, the outer ring includes a tapered surface formed such that the outer ring gradually decreases in thickness from an upstream side toward a downstream side.