To provide a hygienic and compact ball valve with a single seat capable of sealing surely in accordance with fluid pressure put from either direction of fluid passages and producing no oil accumulation in a pocket by providing a ball seat only at one side of valve element.

For a ball valve comprising a valve element 1 to open and close fluid passages 7a, 7b, valve spindle 2 connected to the valve element 1 at the upper and lower portions of the axial direction thereof and making the valve element rotatable, and a ball seat 9 to seal the valve element 1 and the fluid passages 7a, 7b, the valve element 1 is provided with groove sections 3a, 3b to be engaged with the valve spindle 2a, 2b at the upper and lower portions of the axial direction thereof, made to be integrally rotatable in accordance with the rotation of the valve spindle 2 through the contact of the valve spindles 2a, 2b with the side walls of one side end of the groove sections 3a, 3b and also to be floatable to the direction of the fluid passage 7b intersecting perpendicularly to the valve spindles 2a, 2b, and a ball seat 9 to seal a space between the valve element and the fluid passages is provided only in a side wall surface 4a (one fluid passage 7b side of the valve element) of one end side wall of the groove sections 3a, 3b.