A connection device and method of manufacturing the same is provided. The connection device includes a housing including a first face, into which a plug is introduced, and a second face, that is formed to be in contact with the first face; a connection hole extending to the inside of the housing from the first face; an opening extending from the first face to the second face to partially expose the connection hole on at least the second face; and a sealing member arranged on an outer peripheral surface of the housing to surround a region where the opening is formed.