Many insist that the cause of Brexit(Britain's exit from the European Union: Brexit onwards) was the rush of migrants into the UK. However, they seem to neglect something that exists at a deeper level of this phenomenon. Among the possible causes of Brexit at the deeper level, the UK's welfare contradiction is arguably one of the major ones. Thus, this paper aims to explore the relationship between Brexit and welfare contradiction. This paper suggests that deep and surface structural framework of welfare can be applied as an analytical tool. Based on this analytical tool, this article reinvestigates immigrants' welfare and the related welfare contradiction. It covers the benefits, which are allocated to migrants in the UK based on records of National Insurance numbers, the benefits related to council flats and houses for foreign nationals, and health tourism. After these issues are discussed, this paper re-emphasizes the welfare contradiction, which is a deep structure. The implication is that the right of free movement, driven by the phenomenon of globalization, can force the reorganization of a welfare state system based on state sovereignty. Therefore, it is necessary to guarantee the right of movement to the people who are in need, not to impair the welfare state system, rather than to lower the entry barriers as a whole.