To weld an attachment component with sufficient welding strength while suppressing the amount of HC penetration even if a tank body has a regenerative layer.

In a tank body 10, an inner layer 11, an HC barrier layer 12, a regenerative layer 13, and a heat-weldable layer 14 are arranged from the inner side in this order. An annular wall 15 in which an end face 15a thereof is directed outward of a tank, and the inner peripheral surface 15b thereof forms an opening 16 is formed on the tank body 10 in order to weld a vent valve 20 having an annular HC barrier 23 and a heat-weldable section 24 on the outer side thereof. While the annular HC barrier 23 is aligned to the HC barrier layer 12 exposed to the end face 15a of the annular wall 15, the heat-weldable section 24 is welded to the heat-weldable layer 14 with a first annular weld part 31 around the annular wall 15 and a second annular weld part 32 in the annular wall 15.