A connector to be attached to a liquid tank for delivery of its internal liquid, wherein: said connector is constructed of a plug fixedly mounted on said tank and a socket connected with said plug; said plug is provided with: a cup-shaped body having a fitting means for fixing to said tank; a plug tube which has an engagement means (9, 10) engaged with said socket and is vertically provided in a central area of a concave portion of said cup-shaped body such that there is a gap between said plug tube and said cup shaped body; a liquid passage and a gas passage formed in said cup-shaped body to vertically pass through said plug tube: a siphon tube, being a unified portion of said cup-shaped body, integrally formed from the bottom of said cup-shaped body to communicate with the liquid passage; and wherein said socket is provided with: an engagement means engaging with said plug tube; a valve unit; a liquid passage communicated with said liquid passage of said plug tube and a liquid passage connecting piece communicated with said liquid passage of said socket; and a gas passage communicated with said gas passage of said plug tube and a gas passage connecting piece communicated with said gas passage of said socket. said connector is constructed of a plug fixedly mounted on said tank and a socket connected with said plug; said plug is provided with: a cup-shaped body having a fitting means for fixing to said tank; a plug tube which has an engagement means (9, 10) engaged with said socket and is vertically provided in a central area of a concave portion of said cup-shaped body such that there is a gap between said plug tube and said cup shaped body; a liquid passage and a gas passage formed in said cup-shaped body to vertically pass through said plug tube: a siphon tube, being a unified portion of said cup-shaped body, integrally formed from the bottom of said cup-shaped body to communicate with the liquid passage; and wherein said socket is provided with: an engagement means engaging with said plug tube; a valve unit; a liquid passage communicated with said liquid passage of said plug tube and a liquid passage connecting piece communicated with said liquid passage of said socket; and a gas passage communicated with said gas passage of said plug tube and a gas passage connecting piece communicated with said gas passage of said socket. a cup-shaped body having a fitting means for fixing to said tank; a plug tube which has an engagement means (9, 10) engaged with said socket and is vertically provided in a central area of a concave portion of said cup-shaped body such that there is a gap between said plug tube and said cup shaped body; a liquid passage and a gas passage formed in said cup-shaped body to vertically pass through said plug tube: a siphon tube, being a unified portion of said cup-shaped body, integrally formed from the bottom of said cup-shaped body to communicate with the liquid passage; and wherein said socket is provided with: an engagement means engaging with said plug tube; a valve unit; a liquid passage communicated with said liquid passage of said plug tube and a liquid passage connecting piece communicated with said liquid passage of said socket; and a gas passage communicated with said gas passage of said plug tube and a gas passage connecting piece communicated with said gas passage of said socket. a siphon tube, being a unified portion of said cup-shaped body, integrally formed from the bottom of said cup-shaped body to communicate with the liquid passage; and wherein said socket is provided with: an engagement means engaging with said plug tube; a valve unit; a liquid passage communicated with said liquid passage of said plug tube and a liquid passage connecting piece communicated with said liquid passage of said socket; and a gas passage communicated with said gas passage of said plug tube and a gas passage connecting piece communicated with said gas passage of said socket. an engagement means engaging with said plug tube; a valve unit; a liquid passage communicated with said liquid passage of said plug tube and a liquid passage connecting piece communicated with said liquid passage of said socket; and a gas passage communicated with said gas passage of said plug tube and a gas passage connecting piece communicated with said gas passage of said socket.