Device for seperating gas from liquid

A gas-liquid separating apparatus capable of sufficiently separating gas in gas-liquid mixture fluid from liquid therein, is disclosed. Gas-liquid mixture fluid fed from a boiler evaporator tube enters through a separator inlet 15 into a cylinder 9 of a separator 12 in a tangential direction, thus becomes a rotating flow 8 along the inner wall surface of the cylinder 9, and thereby centrifugal separation between gas and liquid is effected. The separated steam is discharged from a secondary separator 11 through a cap 18 into a gas-phase section within a drum 1. A part of the primary isolated water 8 of the rotating flow has its outflow velocity decelerated by a perforated plate 23, and thereafter flows out to a liquid-phase section within the drum 1. As a result, a flow velocity of the primary isolated water 20 flowing out through a primary isolated water outlet 17 to the liquid-phase section within the drum 1 is decreased as compared to the case where the prior art was employed, and hence, an amount of the primary isolated water drawn into a flow 22 within the drum is reduced. Moreover, since the primary isolated water 21 having flowed out through the perforated plate 23 to the liquid-phase section within the drum 1 has a slow outflow velocity, it becomes an upward blow in the vicinity of the cylinder 9 due to influence of a buoyancy acting upon a steam component. Accordingly, the time available for gravitational separation of gas and liquid in the liquid phase within the drum 1 can be reserved longer than in the case of employing the prior art.