A connector includes an outer melt-bonding projection 2 integrally formed with a projecting end 10a of a flange 10 of a base member 1, and an inner melt-bonding member 3 having an upper side 30 unified to a lower surface 10g of the flange 10 of the base member 1 and configured to have an outer lateral side 31 unified to an inner lateral side 20 of the outer melt-bonding projection 2. The outer melt-bonding projection 2 is formed of a first synthetic resin, which is melt-bondable to an outer layer Ta of a fuel tank T, the base member 1 is formed of a second synthetic resin difficult to pass a gas produced from fuel therethrough and adaptable to the first synthetic resin, and the inner melt-bonding member 3 is formed of the first synthetic resin.