To provide a ball valve having no danger of fluid in an outlet passage leaking into a ball valve body even if a pressure of the fluid in the outlet passage blocked by the ball valve body is higher than a pressure of fluid in the ball valve body, and capable of securing a large flow rate without enlarging the valve.

The ball valve 1 is equipped with the ball valve body 5 having an inflow passage (an inflow port ) 5d and an outflow passage (an internal space) 5f and comprising an elastic body, and a valve case 2 having a valve chamber 4 rotatably housing the valve ball body 5 and an inlet flow passage 7 and a plurality of outlet flow passages 8, 9 communicated with the valve chamber 4. The inflow passage 5d is communicated with the inlet flow passage 7 at all times, and the outflow passage 5f is alternatively communicated with either one of the plurality of outlet flow passages 8, 9 by rotation of the ball valve body 5. The ball valve body 5 is equipped with a reinforcement member 6 deformed by a pressure received from a fluid in the blocked outlet flow passage 8 and preventing leaking of the fluid into the ball vale body 5.