To simplify the structure of a valve and a switching operation, and facilitate the reduction of a space when attaching a piping and maintenance/control, by automatically rotating a valve element to a predetermined position by the use of a single selector valve having weak fluid resistance regardless of a normal period and an emergency/abnormal period.

A selector valve is formed by a four-way opening selector butterfly valve 20 in which one circular plate-like valve element 28 whose outside diameter is formed into a complete round is arranged in a spherical main body 26 equipped with fluid outlets/inlets 26A-D arranged in four directions and connected respectively to an upstream main pipe 21, an upstream branch pipe 22 connected to a water storage tank inlet 25a, a downstream main pipe 24 and a downstream branch pipe 23 connected to a water storage tank outlet 25b; the circular plate-like valve element 28 is rotated by a hydraulic actuator equipped with a water pressure operation part introducing an operation source from the downstream or upstream main pipe and changed/operated by two self-operated two-way valves whose opening/closing action is mutually reversed; and the four-way fluid outlets/inlets 26A-D of the four-way selector butterfly valve 20 are changed automatically according to a normal period and an abnormal period.