An endoscope system includes an endoscope (11) and a cleaning adapter (60) or connector. The endoscope has a port device (42) or end sleeve, to which the cleaning adapter is coupled. The cleaning adapter includes a connector housing (61) and a coupling sleeve (62), which has a male tapered portion (63). The connector housing includes a female thread (66) (fastening device) and a guide surface (67). The port device includes a flange (42a) and a male thread (42b). The guide surface guides the port device by contacting the flange. Thus, a male tapered surface (63a) or tapered sealing surface is axially aligned with a female tapered surface (43a) or tapered bore surface. The male tapered surface tightly contacts the female tapered surface by threaded engagement between the male and female threads. Accordingly, air-tightness or liquid-tightness can be ensured even in use of a plurality of connectors couplable selectively for connecting a related apparatus.
