To provide an inexpensive ball valve by fitting a seal member to only a part of a hemispherical valve, and allowing the easy replacement thereof.

Horizontal communication holes 14 and 16 as well as a shaft hole 13 open to hemispherical hollow space 18 are drilled through a case 12, and a plug 20 is inserted in the hollow space 18 from the lower end thereof. The valve spindle 36 of the plug 20 is coupled to the shaft hole 13, and a hemispherical valve 22 is coupled to the hollow space 18. Furthermore, a cover 32 is detachably coupled and fixed to the lower end of the hollow space 18, thereby supporting the valve 22 on the cover 32. Also, the communication holes 14 and 16, and a connection hole 24 formed on the valve 22 are communicated to and isolated from one another via the turning motion of a valve spindle 36. Seal members 66 and 68 are also coupled to and held on recesses 62 and 64 formed on the external surface of the valve 22, and the communication holes 14 and 16 are thereby covered at the time of isolation.