PURPOSE: To eliminate sliding so as to reduce wear by providing first, second and third sealing members respectively between a body and a valve element, between the valve element and a valve guard, and between the body and a male coupling in the cylindrical body of a female coupling, and making the third sealing member replaceable.

CONSTITUTION: A cylindrical coupler body 11 has a valve opened/closed by insertion/detachment of a nipple 30. The valve is composed of a valve guard 12, a valve element 16 and a compression spring 22. The valve guard 12 comprises a seal part 12a and a bar-like support part 12b and has a second sealing member 13. A first sealing member 21 is fitted to the outer periphery of the valve element 16. A third sealing member 26 is detachably fitted into the vicinity of an insert port 27 of the inner surface of the coupler body 11. When a nipple body 31 is inserted, an abutting surface 43 moves the valve element 16, and s seal face 20 is separated from the second sealing member 13 to open a passage of a coupler 10. There is no sliding of each sealing member, so that there is hardly wear.