To maintain the gas barrier characteristic even if a fuel supplying tube is damaged autside by using modified polyethylene resin for outer layer, and using for inner layer any one of polyamide-based resin, ethylene vinyl alcohol and elastomer thereof having gas barrier characteristic.

A fuel supplying tube 21 is integrally formed from a supplying port 21a to a connection part 24 by double-layer bowing or extruding. In this case, thick modified polyethylene resin is used for outer layer 22 so as to give strength, and any one of polyamide-based resin, ethylene vinyl alcohol and elastomer thereof having high gas barrier characteristic is used for inner layer 2b, and the inner and the outer layers are fused for adhesion while extruded from a head by a double-layer blowing machine, and air blowing is performed in a die so as to form a fuel supplying tube body 22 of double-layer hollow body. With this structure, even if the fuel supplying tube 21 is damaged outside, since the inner layer 22b works as a gas barrier layer, it 21 is not damaged, and any influence is not given to the gas transmission.