NOVELTY - The turbine i.e. air turbine (25), has a main shaft (26) installed to face an inner peripheral side of a nozzle-ring assembly (43), where the main shaft is rotationally driven by airflow. A floating shutter (47) is raised/lowered to an outer peripheral side of the nozzle-ring assembly. An airflow control mechanism (39) selectively switches airflow from an exterior and an air chamber (18), where airflow in an outer peripheral part of a partition assembly (40) is guided as one-way turning-inward flow through the nozzle-ring assembly and a radial-flow type impeller (27).    USE - Turbine i.e. air turbine, for driving a wave activated generator for generating wave-powered electricity in a cylindrical shape floating body anchored to seawater.    ADVANTAGE - The airflow control mechanism selectively switches airflow from the exterior and the air chamber such that airflow in the outer peripheral part of the partition assembly is guided as the one-way turning-inward flow through the nozzle-ring assembly and the impeller, so that turbine structure and flow-path structure of an airflow can be simplified with reduced weight and formed as a compact cassette type structure, thus reducing manufacture/installation cost of the turbine by assembling the turbine easily, and hence improving maintainability and safety of the turbine without causing impact noise of the shutter. The airflow along the nozzle-ring assembly and the impeller of an installation in the partition assembly to make rotation of the impeller stably by one-way turning-inward flow, thus rotationally driving the main shaft continuously and stably with better availability factor, and hence improving turbine operation efficiency by designing the impeller uniformly, while improving design freedom of the turbine.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) an assembling method for a turbine for wave-powered electricity generation    (2) an operating method for a turbine for wave-powered electricity generation.    DESCRIPTION OF DRAWING(S) - The drawing shows a longitudinal cross-sectional view of a turbine for facilitating wave-powered electricity generation and releasing air from an air chamber to atmosphere.'(Drawing includes non-English language text)'    Air chamber (18)    Air turbine (25)    Main shaft (26)    Radial-flow type impeller (27)    Airflow control mechanism (39)    Partition assembly (40)    Nozzle-ring assembly (43)    Floating shutter (47)