A foam filler is provided with a base for forming a foam and placed inside a hollow structure having a through hole. An opening having an area larger than the opening of the through hole is created in the base and surrounding the through hole. The foam filler is provided with an upper wall which follows the flow and the thermal expansion of the base at the time of heating. The upper wall closes at least part of the opening of the through hole when following the flow and the thermal expansion of the base, and thus prevents the base from entering into the through hole. The upper wall is provided in a peripheral portion of the opening and placed in a part of an area surrounding the through hole.