To provide a seal device provided in a valve device performing opening operation in the case of collecting a refrigerant of an air conditioner, at low costs and with food sealability and easy mounting property.

In a spindle 6 screw mounted by a thread 15 advanceably retractably in a main unit pipe part 7 of a valve device to open/close a passage of refrigerant sealing/collection, a single O ring 18 formed with a sectional shape in a heart or C type with two mountain parts 19a, 19b in continued shape is fit-mounted, and a double seal by the mountain parts 19a, 19b into surface contact with an internal surface of a main unit pipe part 7c can be performed by a single seal member.