This dissertation investigates how labor migration occurs in Japan. While Japan has accepted migrants in the last two decades, under the restrictive regime of immigration, labor migration at the bottom of labor market has mainly occurred through Japan's de facto temporary migrant worker program: the Foreign Trainee/Technical Intern Program. Nevertheless, the demand for migrants through this program is still small nationally, and, moreover, varies locally. Both the literature of labor migration, which takes the Western context of migration for granted, and that of immigration policy, which takes Japan more seriously but focuses on why its immigration policy is restrictive, have failed to engage these puzzles. The dissertation interrogates these issues by looking at the seafood processing industry. This dissertation makes two arguments. First, it argues that migrants are more likely to be brought into seafood processing sites that have gone through what the author calls petite industrialization. While the seafood processing industry may overall be a competitive sector of the economy that needs migrant labor, the demand for migrants is more prominent where the local seafood processing sector has developed a more industrialized production system. The demand for migrants is small and geographically concentrated since petite industrialization is an exception in the industry. Second, it also argues that petite industrialization matters since an imperative of mass production necessitates a stable input of labor for intensive work. Trainees and technical interns are a preferable labor force due to their stability on a year-round basis. This dissertation argues that the concentration of migrants in the petite- industrialized seafood processing industry demonstrates the way this industry has adapted to Japan's labor migration policy as an opportunity structure of labor migration. The dissertation conducts both a quantitative and qualitative analysis. A statistical regression analysis draws upon the dataset constructed from available official datasets. This analysis is supplemented by a qualitative investigation of two seafood processing sites, the data for which was garnered from the author's interviews with seafood processing companies and other relevant informants as well as secondary published materials. The secondary literature is also used for the comparison with the American food processing industry