According to an embodiment, a turbine comprises: a cylindrical casing; and turbine stator blades arranged in the casing along a circumferential direction. The turbine stator blades each includes: a blade effective part; a coolant flow path through which a coolant flows in the blade effective part to cool the blade effective part; an outer ring sidewall provided on an outer periphery of the blade effective part; an inner ring sidewall provided on an inner periphery of the blade effective part; and a contact part provided at an end part of the inner ring sidewall with at least part thereof being along a flow direction of a working fluid, coming into contact with the inner ring sidewall of the adjacent blade during operation, and separating from the inner ring sidewall of the adjacent blade when the operation is stopped.