To provide a means to efficiently obtain a high quality hollow material maintaining a shape of butt joint before joining at the time of manufacturing a hollow material equipped with a hollow part by way of combining both of frameworks by friction stirring welding from a pair of long size materials having a U-shaped cross section continuous in the longitudinal direction.

In a hollow part 20 constituted between frameworks 10, 10 disposed to face oppositely a pair of long size materials 1A, 1A, an internal receiving base 5 equipped with a roller 51 rolling contacting the internal surface of the joining side and a roller 52 rolling contacting the opposite internal surface is loaded, and then both the long size materials 1A, 1A are joined and integrated while being relatively moved against a working head 3 with the internal receiving base 5 positioned near an abutted part of the working head 3 for friction stirring welding by a retaining means 6A.