The present invention is also a ball valve in which a valve chamber with an entrance and exit communicating with each other in a casing is formed, a valve ball with a circulation hole is provided in the valve chamber, an entrance-side ring valve seat is provided on the entrance side and an exit-side ring valve seat is provided on the exit side of the valve ball, the entrance and the exit are connected or disconnected by rotate-operating the valve ball with a valve shaft hermetically passing through the casing, wherein a through hole passing through from a valve ball contact surface to a casing contact surface is formed in the entrance-side ring valve seat, and a discharge orifice with one end communicating the through hole of the entrance-side ring valve seat and the other end communicating ambient air is formed, and wherein a first passage hole which connects the circulation hole with the entrance in a first disconnection state where the valve ball disconnects the entrance from the exit, and which connects the circulation hole with the exit in a second disconnection state where the valve ball is rotated by 180 degrees from the first disconnection state so as to disconnect the entrance from the exit, and a third passage hole which connects the circulation hole with the through hole in the second disconnection state and which is disconnected from the through hole in the entrance-side ring valve seat in the first disconnection state, are formed in the valve ball.

In the ball valve according to these example embodiments of the present invention, in the first disconnection state where the valve ball is rotate-operated to disconnect the entrance from the exit, the entrance, the exit and the discharge orifice are disconnected. In the second disconnection state where the valve ball is rotate-operated by 180 degrees from the first disconnection state, the exit and the discharge orifice communicate with each other through the first passage hole, the circulation hole, the third passage hole and the through hole. In these arrangements, remaining pressure at the exit can be released from the discharge orifice communicating ambient air different from the entrance and exit.