The species appears to be present on all Japanese islands. It inhabits forests, grasslands, and cultivated fields, including rice paddies, at any altitude.Though occupying the same broad ecological niche as A. argenteus, the two species prefer different microhabitats: A. argenteus prefers dense canopy, while A. speciosus prefers open secondary forests. Large Japanese field mice forage primarily at night, likely to avoid predation They are omnivores but mostly known to be seed-eating mice, particularly around autumn and winter, as the mice hoard acorns and walnuts, which comprise 13-100% of their food. This makes them effective seed dispersers. Mast seeding can have serious effects on field mouse populations, including increases in overwinter survival, winter reproduction, and population density.