This thesis examines whether an inflow of foreigners threatens Japanese public safety by conducting regression analysis. In order to maintain the current level of economic activity, Japan may have to rethink its closed immigration policy. However, the debate for immigration policy is not so hot so far. Moreover, the studies regarding socioeconomic impacts of immigrants on Japanese society are insufficient. Rather they have not been examined carefully and extensively. The thesis tries to fill this gap. The thesis, exploring the changes in crime and immigration rates in Japan from 1995 to 2006, partly applies basic frameworks of the past research developed in the United States for examining the relationship between crime and immigration. In particular, using Japanese data (e.g., Population Census and Crime Statistics Report) in a pooled cross-section, it examines changes in prefectural crime and immigration rates in Japan from 1995 to 2006 with fixed-effects models to test whether immigration and crime are really positively related as Japanese society believe. The study finds that the increase of immigration in a prefecture (1) may be positively correlated with felonious violent crime rates, (2) but not related to total and property crime rates in Japan. In order to minimize this negative impact of immigration on Japanese society, the thesis suggests that additional governmental efforts are necessary to mitigate the consequences (e.g. establishing Immigration Agency which is responsible for entire Japanese immigration policy from legal admission to social integration for newly admitted immigrants).