To provide a ball valve capable of preventing a valve element and holding member from protruding from inside of a valve body.

An arcuate female screw part 31 threadedly engageable with a male screw part 30 which is protruded toward the inside of the body 12 from each part, extended in a peripheral direction of the body 12 and formed in a holding member 23, is formed in parts facing respective plane parts 21a, 21b and each opening 20a of a flow passage hole 20 in a valve element 13 on the inner peripheral surface 12b of the body 12 when inserting the valve element 13 into the body 12. A protruded amount of each female screw part 31 facing each opening 20a is set to keep the minimum value of a space between both female screw parts larger than the length of the flow passage hole 20 in the valve element 13 along the axial line thereof. A protruded amount of each female screw part 31 facing each plane part 21a, 21b is set to keep the minimum value of a space between both female screw parts larger than a space between both plane parts 21a, 21b.