A ball valve which can suppress the increasing of processing labor time and reliably prevent simultaneous rotation of a ball seat and a ball when the ball is rotated by handle manipulation is provided. The valve body 2 is formed of a hard material such as stainless steel, the ball seat is formed of a relatively soft material such as a fluorine resin, and a protrusion 18 is formed on a ball seat support surface 13 of the valve body 2 made of a hard material so as to bite into the ball seat 4.