An adapter (100) has a through hole (103). A first end portion (101) of the adapter includes a tubular portion (110) on which a first projection (111) and a second projection (112) are provided. The adapter can be connected to a male connector at a first position where a claw (32) of the male connector is engaged with the first projection (111) and at a second position where the claw (32) is engaged with the second projection (112). When the adapter is connected at the first position, a flow channel (11) of a male member (10) is sealed with a cover (4). When the adapter is connected at the second position, the adapter compressively deforms an outer circumferential wall (45) of the cover so that the flow channel of the male member is in communication with the through hole (103) of the adapter.
