Abstract: A method and an apparatus for opening/closing a valve are provided. The method includes the steps of varying a position of a seat assembled into an inner side of a fluid passage of a valve body using a pneumatic pressure or a magnetic force so as to be separated from a turning radius of a valve member for opening/closing the fluid passage, rotating the valve member in a forward or reverse direction by an actuator, rotating the valve member in the forward direction and opening the fluid passage, rotating the valve member in the reverse direction, and returning the position of the seat so that an inner side of the seat is sealingly contacted with an outer face of the valve member and closing the fluid passage.