Provided is an adapter (100) that has a through hole (103). A first end (101) of the adapter has a cylindrical part (110) to which a first protrusion (111) and a second protrusion (112) are provided. The adapter can connect to a male connecter at a first position at which a claw (32) of the male connector engages with the first protrusion (111), and at a second position at which the claw (32) engages with the second protrusion (112). When the adapter is connected at the first position, a channel (11) of a male member (10) is sealed by a cover (4). When the adapter is connected at the second position, the adapter compressively deforms an outer peripheral wall (45) of the cover so that the channel of the male member communicates with the through hole (103) of the adapter.
