Due to its aging population, Japan has been experiencing the negative effects of a shrinking workforce. Relaxing immigration policies and increasing the number of foreign workers has been suggested to help alleviate the workforce problem. This paper explores the circumstances under which the Japanese public is likely to hold favorable attitudes toward open immigration. Using intergroup contact and group threat theories, we determine that there is a conditional relationship between the frequency of contact with foreigners and the number of foreigners in a region on attitudes toward immigration. As the size of the foreign population increases, frequency of contact with foreign workers no longer has a mediating effect on immigration attitudes, and support for more open immigration policies decreases.