PURPOSE: To supply a ball valve full open flow rate set at an initial stage for a long period of time.

CONSTITUTION: A nozzle hole 1E is opened toward the lower end of a housing 1 from the lower end of a valve seat 1C, and a full open flow rate regulating hole 8 is opened upward from the upper end of the valve seat 1C. An effective opening area Se of the nozzle hole 1E, an effective opening area Sc formed by a valve part 6A of a ball valve 6 and the valve seat 1C at the time of stroking of the ball valve 6 the valve part, 6A of which is separated from the valve seat 1C and an effective opening area Sf formed by an outer diametrical part 6B of the ball valve 6 and the full open flow rate regulating hole 8 at the time of stroking of the ball valve 6 are specified as Sf<So and Sf<Se.