Fossil benthic foraminifera from a sediment core taken from central Lake Shinji, western Japan, were investigated as an indicator of paleoenvironmental change in the Shinjiko-Nakaumi lake system during the 20th century. A transition from dominance of Haplophragmoides canariensis to that of Ammonia beccarii forma 1 occurred in the middle 20th century. This faunal association and its transition are similar to those observed in previous studies of Lake Shinji and the Ohashi River. This faunal transition might be affected by not only environmental change in Lake Shinji but also that in the Ohashi River.