Japanese spotted fever (JSF) is a rickettsial disease caused by Rickettsia japonica. To the best of our knowledge, there have only been five reported cases of JSF involving the central nervous system. A 74-year-old man was admitted after 1 week of fever and maculopapular rash. JSF was definitively diagnosed by PCR; however, the patient showed mental disturbance and abnormal behavior. After intravenous immunoglobulin, his mental state and behavior improved. The findings of cerebrospinal fluid analysis, electroencephalography, and 99 mTcHM-PAO single photon computed emission tomography suggested post-infectious encephalitis. JSF causes post-infectious encephalitis and early treatment is recommended.