To provide a ball valve with internal components incorporated therein in a correctly mounted condition for reliably developing high sealing performance and allowing assembling/disassembling work while preventing damage to the components.

In the ball valve, a lower opening portion 14 is provided in the lower position of a body 11 having a primary and secondary flow paths 12, 13 on the right and left sides, a ball valve element 20 having an operation shaft 25 inserted through the lower opening portion 14 and upper and lower stems 21, 22 is turnably provided in the body 11, and seat retainers 30 are provided at the front ends of flow path pipes 40, 41 connected to the primary and secondary flow paths 12, 13, respectively. Ball seats 33 are mounted on the seat retainers 30, and the ball seats 33 are thrust via a spring mechanism 32 in contact with a ball face 20d of the ball valve element 20. A front end 51 of a plug 50 for blocking the lower opening portion 14 is arranged adjacent to a bottom 24 of the ball valve element 20.