A foam filling member having a foaming base material in sheet form which is simplified in structure so that it can be formed into a predetermined shape corresponding to a shape of a space of a structure with an improved working efficiency and can also be placed in a space of the structure with an improved working efficiency, without any need of the sticking to a wall surface of a partition wall defining the space of the structure. Incisions 4, 5, 6, 7, cut in partway along a thickness direction of the foaming base material 2 along a bending portion and cuts 9, 10 passing through in the thickness direction are formed in the foaming base material 2. By simply bending or folding the foaming base material 2 along the incisions 4, 5, 6, 7 and the cuts 9, 10, the foam filling member 1 can be formed in a three-dimensional shape corresponding to an interior space of a pillar and thus can be set in place in the interior space. By foaming the foaming base material 2 thus placed in the interior space, the foam can be filled up in the interior space, leaving no space therein.