Piping unit for transporting a fuel is constructed by connecting a resin tube and a connector for connecting the resin tube to a mating pipe. The connector has a connector body including a retainer holding portion and a retainer for engaging with the mating pipe. The resin tube has a multilayered construction including an inner fuel barrier layer and an outer layer covered with a protective layer. The outer layer has a small outer diameter (od) up to 6 mm, the fuel barrier layer and the outer layer have a wall-thickness (t), and a ratio of the outer diameter (od)/the wall thickness (t) is in a range of 4 to 8.