Turbine and turbocharger

A turbine, comprising:

• a turbine impeller;
• a plurality of nozzle vanes, which are placed on a radially outer side with respect to the turbine impeller so as to be spaced apart from each other in a circumferential direction of the turbine impeller, and are each provided so as to be pivotable about a pivot axis extending along an axial direction of the turbine impeller;
• a blade shaft, which protrudes from each of the plurality of nozzle vanes in the axial direction, and is provided so as to be turnable integrally with each of the plurality of nozzle vanes;
• an annular member, which extends in the circumferential direction, and is opposed to the plurality of nozzle vanes in the axial direction;
• a plurality of blade shaft holes that open in a first surface of the annular member that is opposed to the plurality of nozzle vanes, the plurality of blade shaft holes being formed apart from each other in the circumferential direction, the plurality of blade shaft holes each allowing the blade shaft to be inserted into the blade shaft hole and each having a bottom surface;
• and
• an annular protruding portion that is provided on an inner peripheral side of a second surface of the annular member on a side opposite to the first surface, the annular protruding portion extending in the circumferential direction and protruding in the axial direction.